6. Graphing Piecewise and Step Functions
Sign In
An error ocurred, try again later!
Chapter 5
6.
Graphing Piecewise and Step Functions
Understanding piecewise and step functions is crucial in mathematics. These functions are defined differently for various parts of their domains, often using intervals or inequalities. For instance, a piecewise function might describe a person's distance from home over time, considering different speeds and activities. Similarly, a step function can represent the number of items collected over a week, with each day having a distinct value. Graphing these functions requires attention to each segment, ensuring accurate representation. Such functions have practical applications, like determining parking charges based on hours or tracking daily tips received by a server. By mastering these concepts, one can tackle real-world problems with ease.
Show less Show more expand_more Lesson Settings & Tools
| | 14 Theory slides |
| | 8 Exercises - Grade E - A |
| | Each lesson is meant to take 1-2 classroom sessions |
The aim of this lesson is to graph functions that are defined differently for different parts of their domains.
Catch-Up and Review
Here are a few recommended readings before getting started with this lesson.
Challenge
How Many Cans Are There in the Fridge?
Mark always likes to have cans of his favorite soft drink in the refrigerator so that he can enjoy a cold drink whenever he wants.
At the beginning of the week, he had 11 cans in the fridge. Over the week, Mark wrote down each time cans were consumed or added.
- On Monday, Mark drank 1 can.
- On Wednesday, Mark bought 2 cans at a convenience store and put them into the fridge.
- On Friday, Mark had a party and a total of 10 cans were consumed.
- On Saturday, Mark bought a 12-pack of soda from a supermarket and put them away in the refrigerator.
a How can the number of cans in the fridge be written as a function?
b Graph the number of cans in the refrigerator over the week.
Discussion
Piecewise Functions
A piecewise function is a function that is defined differently for different parts of its domain. These functions are commonly defined using intervals or inequalities. Consider the following example.
For every function, each input can correspond to only one output. Therefore, when two pieces of a piecewise function share a limit value, only one of the pieces can be defined for that value. It can be seen in the example function for f that only the second piece is defined for x=0. Additionally, it is possible for a piecewise function to be undefined for some intervals.
f(x)={-x−2,2x+1,if x<0if x≥0
This function is defined as one linear function for values of x less than 0, and a different linear function for values of x that are at least zero. The graph of f is obtained by graphing the two rays. It should be noted that both rays represent the same function. Pop Quiz
Practice Finding Values
A piecewise function f is shown below. For every given value of x, find the correct value of f(x). Round the result to two decimal places, if necessary.
Discussion
Graphing Piecewise Functions
When graphing a piecewise function, each piece must be considered separately. First, a piece is graphed for the values of its domain. Then an end — or ends — of the piece are marked with one of the following.
- A closed circle for an x-value for which the function is defined.
- An open circle for an x-value for which the function is undefined.
f(x)={4x+6,-x+3,if x≤-1if x>-1
Now, each piece will be considered one at a time. Then, the graphs will be combined.
1
First Piece
expand_more The first piece is f(x)=4x+6. This is a linear function written in slope-intercept form. The function can be graphed by using the y-intercept and the slope.
Now, since the function is limited to inputs less than or equal to -1, the line will be graphed until it reaches x=-1. Since the inequality x≤-1 is non-strict, the function is defined for x=-1 and the circle will be closed.
2
Second Piece
expand_more A similar process can be repeated to graph the second piece f(x)=-x+3. First, the line will be graphed.
This piece is defined for values of x greater than -1. This means that the line will be drawn starting at x=-1. Also, since the inequality is strict, the circle will be open.
3
Combining the Graphs
expand_more Finally, the pieces will be graphed together in the same coordinate plane to complete the graph. It is important to pay attention to the limit points, since each value of x must be assigned to only one value of the function.
Example
Going to the Beach
On his summer vacation, Heichi often rides his bike to a nearby beach. Today he is going to meet a friend there.
After leaving his house, Heichi bikes at 15 miles per hour for one hour until he reaches the beach. He spends 5 hours at the beach, then goes back to his house at 10 miles per hour. He arrives at back home an hour and a half after leaving the beach.
a Write a piecewise function that describes Heichi's distance from home as a function of time.
b Graph the function written in Part A.
Answer
a f(t)=⎩⎪⎪⎨⎪⎪⎧15t,15,-10t+75,if 0≤t≤1if 1<t≤6if 6<t≤7.5
b 
c The domain consists of the number of hours betweeen 0 and 7.5 hours. The range is all the possible distances between 0 and 15 miles from his house.
Hint
a Determine a function rule for each part of Heichi's trip.
b Graph each piece one at a time.
c Where does the function written in Part A start? Where does it end?
Solution
a To begin with, for the first hour, Heichi bikes at 15 miles per hour. This speed can be used to write the first piece of the desired function. It is important to remember that the distance traveled is the product of the speed and the travel time.
f(t)=⎩⎪⎪⎨⎪⎪⎧15t,??if 0≤t≤1
Since Heichi was biking at 15 miles per hour for one hour, he traveled 15 miles in this interval. In the next piece, the value of the function is constant at 15 for the values of t between 1 and 6 because he is just hanging out at the beach for these 5 hours.
f(t)=⎩⎪⎪⎨⎪⎪⎧15t,15,?if 0≤t≤1if 1<t≤6
Finally, when Heichi goes home, he bikes at 10 miles per hour. Since he is returning home, the distance from his house will decrease. Therefore, the distance traveled is written as the product of -10 and t. -10t
Also, since Heichi arrives at home one and a half hours later, the final value of the last piece should be 7.5 hours after the beginning of the trip. Therefore, the function needs to be translated 7.5 units right by subtracting 7.5 from t before multiplying by -10.
-10(t−7.5)=-10t+75
Finally, it is possible to write the complete function rule by adding this final piece.
f(t)=⎩⎪⎪⎨⎪⎪⎧15t,15,-10t+75,if 0≤t≤1if 1<t≤6if 6<t≤7.5
b To graph the obtained piecewise function, each piece will be graphed one at a time on the same coordinate plane. First, the graph of 15t from 0 to 1 can be drawn by using the slope 15 and the y-intercept 0. Since the limit inequalities are non-strict, the border points will be closed.
The second piece of the function is the horizontal line f(t)=15. Also, since the inequality is non-strict, the circle at t=6 will be filled.
Now, the x-intercept can be used to graph the third and final piece. From Part A, it is known that the x-intercept is 7.5.
Finally, the graph of the piecewise function is completed.
c From Part A, it can be seen that the function is defined for times between 0 and 7.5 hours, inclusive. Therefore, the domain of the function consists of all the real numbers in that interval.
Domain[0,7.5]
The function's output represents how far Heichi is from his house. Looking at the graph, it can be seen that the minimum value of the function is 0, when Heichi is at his house, and the maximum value is 15, when Heichi is at the beach. While he is biking between his house and the beach, all distances from 0 to 15 are reached. Range[0,15]
Discussion
Step Functions
A step function is a piecewise function that is defined by a constant value on each part of its domain. As an example, consider the following function.
f(x)=⎩⎪⎪⎪⎪⎨⎪⎪⎪⎪⎧0,2,4,6,if 0≤x<1if 1≤x<2if 2≤x<3if 3≤x<4
The graph of a step function consists of horizontal line segments, which can be interpreted as steps. The graph of the given function has four line segments. Example
Collecting Boxes Over the Week
As a summer activity, Tearrik participates in charity events for his community. He is volunteering for a food drive event this weekend.
He went to a shopping center multiple times over the week to collect boxes of food for the food drive. On each day, he collected the following number of boxes.
- 5 boxes on Monday
- 3 boxes on Tuesday
- 2 boxes on Wednesday
- 3 boxes on Thursday
- 4 boxes on Friday
Answer
f(x)=⎩⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨⎪⎪⎪⎪⎪⎪⎪⎪⎪⎧0,5,8,10,13,17,if 0≤x<1if 1≤x<2if 2≤x<3if 3≤x<4if 4≤x<5if 5≤x<6
Solution
First, the domain of the function must be determined. The domain can be defined as the given days of the week, starting with the Sunday before Tearrik started collecting the boxes as x=0. Since Tearrik makes his first pickup on Monday, he starts with zero boxes on Sunday x=0.
Finally, the function rule of the step function can be written based on the table.
f(x)=0,if 0≤x<1
On Monday, since one day has passed from Sunday, x=1. On this day, Tearrik collected his first 5 boxes. f(x)=5,if 1≤x<2
On the following days, Tearrik collected more boxes. The boxes picked up each day were added to the number of boxes collected previously. Using this information, the pieces can be written in a table. | Day | Collected Boxes | Boxes in Total | x | f(x) |
|---|---|---|---|---|
| Sunday | - | 0 | 0≤x<1 | 0 |
| Monday | 5 | 0+5=5 | 1≤x<2 | 5 |
| Tuesday | 3 | 5+3=8 | 2≤x<3 | 8 |
| Wednesday | 2 | 8+2=10 | 3≤x<4 | 10 |
| Thursday | 3 | 10+3=13 | 4≤x<5 | 13 |
| Friday | 4 | 13+4=17 | 5≤x<6 | 17 |
f(x)=⎩⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨⎪⎪⎪⎪⎪⎪⎪⎪⎪⎧0,5,8,10,13,17,if 0≤x<1if 1≤x<2if 2≤x<3if 3≤x<4if 4≤x<5if 5≤x<6
Discussion
Graphing Step Functions
Since step functions are piecewise functions, to graph them, each piece must be considered separately. First, each piece is graphed in its domain as a part of a horizontal line. The end or ends are then marked with one of the following.
- A closed circle for an endpoint that is included in the function rule.
- An open circle for an endpoint that is not included in the function rule.
f(x)=⎩⎪⎪⎨⎪⎪⎧1,3,5,if 0≤x<2if 2≤x<4if 4≤x<6
For this example, one piece will be graphed in detail, then the other pieces will be graphed by following a similar process.
1
Graph a Horizontal Line
expand_more The first piece is defined over the interval 0≤x<2. This piece will be graphed by drawing a horizontal line at y=1 from x=0 to x=2.
2
Drawing Endpoints
expand_more It can be noted that x=0 is included in the domain of the first piece, but x=2 is not. Therefore, the left end of the segment will be marked with a closed circle and the right end with an open circle.
3
Graph the Other Pieces
expand_more Then, the same process is repeated for each piece of the function.
Example
Saving Tips for a Week
Zain is working as a server in a restaurant for a week before their summer vacation ends.
Most of their payment comes from the tips they receive. Zain made note of how much they received in tips, starting from Monday and through their last day working on Saturday.
- $49.50 on Monday
- $38.17 on Tuesday
- $41.45 on Wednesday
- $58.33 on Thursday
- $60.55 on Friday
- $57.00 on Saturday
a Write a step function that describes the tips that Zain received during the week.
b Graph the function written in Part A.
Answer
a f(x)=⎩⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎧0,49.50,87.67,129.12,187.45,248.00,305.00,if 0≤x<1if 1≤x<2if 2≤x<3if 3≤x<4if 4≤x<5if 5≤x<6if 6≤x<7
b 
Hint
a Determine the domain of the function.
b Graph each piece separately.
Solution
a The first thing to consider when writing a function is the domain. The domain of this function is defined as the days of the week, starting from the Sunday before Zain's week of work. This Sunday will be marked as x=0. Each day of the week will correspond to the next consecutive integer.
f(x)=0,if 0≤x<1
This indicates that Zain received $0 in tips on Sunday before they start working. On Monday x=1, Zain received $49.50 in tips. This defines the next piece of the function.
f(x)=49.50,if 1≤x<2
Since the function reflects the total amount of money Zain receives in tips, the value of each of the pieces can be determined by adding the new tip value to the total tip amount from the day before. Using this information, the pieces can be written in a table. | Day | Tips Received | Total Tips | x | f(x) |
|---|---|---|---|---|
| Sunday | - | 0 | 0≤x<1 | 0 |
| Monday | 49.50 | 0+49.50=49.50 | 1≤x<2 | 49.50 |
| Tuesday | 38.17 | 49.50+38.17=87.67 | 2≤x<3 | 87.67 |
| Wednesday | 41.45 | 87.67+41.45=129.12 | 3≤x<4 | 129.12 |
| Thursday | 58.33 | 129.12+58.33=187.45 | 4≤x<5 | 187.45 |
| Friday | 60.55 | 187.45+60.55=248.00 | 5≤x<6 | 248.00 |
| Saturday | 57.00 | 248.00+57.00=305.00 | 6≤x<7 | 305.00 |
f(x)=⎩⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎨⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎧0,49.50,87.67,129.12,187.45,248.00,305.00,if 0≤x<1if 1≤x<2if 2≤x<3if 3≤x<4if 4≤x<5if 5≤x<6if 6≤x<7
b To graph a step function, each piece should be graphed separately on the same coordinate plane. The first section is a horizontal line at 0, limited to x=0 and x=1. The first circle will be closed and the second will be open.
The next piece is the horizontal segment at 49.50 with a closed endpoint at x=1 and an open endpoint at x=2.
The remaining pieces can be added to the graph by following the same process.
Discussion
Greatest Integer Function
The greatest integer function, also known as the floor function, assigns the largest integer that is less than or equal to the value of x. This function is usually written as f(x)=⌊x⌋ or f(x)=∥x∥. Consider the following examples.
The domain of the function is the set of all real numbers, but its range is the set of integers. A filled point indicates that the point is part of the graph, while an open point indicates that it is not.
⌊-2⌋⌊-1.5⌋⌊-0.01⌋⌊1⌋⌊1.25⌋=-2=-2=-1=1=1
It can be noted that if x is an integer, the function returns the same value. ⌊-2⌋=-2⌊0⌋=0⌊1⌋=1
Otherwise, it returns the closest integer at the left of x in a number line. Considering more values can help understand how to draw the graph of the function.
| x | f(x)=⌊x⌋ |
|---|---|
| -1 | -1 |
| -0.75 | -1 |
| -0.5 | -1 |
| -0.25 | -1 |
| 0 | 0 |
| 0.5 | 0 |
| 1 | 1 |
| 1.25 | 1 |
| 1.75 | 1 |
| 1.99 | 1 |
| 2 | 2 |
From the table above, it can be seen that the function only changes its value when a new integer is reached. It can be noted that the greatest integer function is a step function. Its graph is presented as follows.
Example
The Price of Parking at the Cinema
Dominika is going to a movie at a local theater on her last day of vacation.
The cost to park in the theater lot is $10 for less than an hour. An additional $2.50 is charged for each hour of parking.
a Write the greatest integer function that describes the prices of the mall's parking lot.
b Graph the function obtained in Part A.
Answer
a
f(x)=2.5⌊x⌋+10
b
Hint
a If $2.50 is charged every hour, only the integer part of the number of hours determines parking charges.
b Start with the graph of the greatest integer function. Then, apply transformations to modify the graph.
Solution
a The first thing to notice to write the function is that $2.50 is charged for each hour of parking. This means that as soon as one hour is reached, $2.50 is added to the total cost of parking. At the two hour mark, the next $2.50 is charged. This can be written by multiplying ⌊x⌋ by 2.5, where x is the parking time in hours.
f1(x)=2.5⌊x⌋
Additionally, the lot requires an initial payment of $10 for the first 59 minutes of parking. This information can be used to add 10 to the value of the obtained function f1.
f(x)=2.5⌊x⌋+10
This completes the required function, as the price to enter is considered and $2.50 is added as each hour is reached.
b This function can be graphed by modifying the graph of the greatest integer function. Since only the positive values of x are relevant, the graph will be considered only in the first quadrant. This graph is shown as follows.
Next, since the greatest integer function is multiplied by 2.5, each value of y is multiplied by 2.5, vertically stretching the spaces between each horizontal segment.
Then, since 10 is added to the product, each segment is translated vertically 10 units up.
Finally, the scope of the coordinate plane will be adjusted so that more steps of the graph can be seen.
Example
Math Graphing Assignment
During his summer vacation, Ignacio went to private math lessons. After learning about the greatest integer function, Ignacio was asked by his math tutor to graph the numbers y greater than or equal to ⌊x⌋.
Answer
Hint
Graph the greatest integer function. Then, determine the solution set by shading the appropriate region.
Solution
The first step to graph an inequality is to graph the border function. The border function of the given inequality is given by the greatest integer function. This function is a step function whose output is the greatest integer less than or equal to the input x. Note that the inequality is non-strict, so the horizontal lines are drawn as solid lines.
Finally, the following is the complete graph of the inequality that the teacher asked for.
Closure
Cans in the Fridge
At the beginning of this lesson, it was asked that a function for the number of soda cans in Mark's refrigerator be written. Mark starts the week with 11 cans in the fridge and then does the following.
- On Monday, Mark drank 1 can.
- On Wednesday, Mark bought 2 cans at a convenience store and put them into the fridge.
- On Friday, Mark had a party and a total of 10 cans were consumed.
- On Saturday, Mark bought a 12-pack of soda from a supermarket and put them away in the refrigerator.
a How can the number of cans in the fridge be written as a function?
b Graph the number of cans in the refrigerator over the week.
Answer
a f(x)=⎩⎪⎪⎪⎪⎪⎪⎪⎨⎪⎪⎪⎪⎪⎪⎪⎧11,10,12,2,14,if 0≤x<1if 1≤x<3if 3≤x<5if 5≤x<6if 6≤x<7
b
Solution
a The first thing to do when writing a function is to determine its domain. In this case, the domain can be written as the number of days passed from the beginning of the week, starting from Sunday as x=0. With the given information, it is possible to write the first part of the piecewise function.
f(x)=11,if 0≤x<1
Mark drank one can of soda on Monday. Therefore, he has now 11−1=10 cans left in the fridge that day. Also, since he neither drank nor bought any soda on Tuesday, the function's output is still 10 until Wednesday, when x=3.
f(x)=10,if 1≤x<3
Mark bought 2 cans on Wednesday, meaning that there are 10+2=12 cans of soda in the fridge that day. Since he neither bought nor drank any of the soda in the refrigerator on Thursday, he has 12 cans until Friday.
f(x)=12,if 3≤x<5
At Friday's party, a total of 10 cans were drunk. Therefore, he has 12−10=2 cans left in the refrigerator for Saturday. Then, on Saturday, he bought a 12-pack of soda cans, making it for 2+12=14 cans in the refrigerator for that day. Because no more information was given, the whole function rule can now be written.
f(x)=⎩⎪⎪⎪⎪⎪⎪⎪⎨⎪⎪⎪⎪⎪⎪⎪⎧11,10,12,2,14,if 0≤x<1if 1≤x<3if 3≤x<5if 5≤x<6if 6≤x<7
b Since every part of this function is a constant value, this is a step function. The graph of a step function consists of horizontal lines limited to specific inputs. It is important to remember the values for which the inequality for x is strict or non-strict.
f(x)=⎩⎪⎪⎪⎪⎨⎪⎪⎪⎪⎧2x−3,-3x,6,x+6,if x≤-3if -3<x≤0if 0<x≤2if x>2
{"type":"text","form":{"type":"math","options":{"comparison":"1","nofractofloat":false,"keypad":{"simple":true,"useShortLog":false,"variables":[],"constants":[]},"rendered":false},"text":"<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><\/span><\/span>"},"formTextBefore":"<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:2.40003em;vertical-align:-0.95003em;\"><\/span><span class=\"mord mathdefault\" style=\"margin-right:0.10764em;\">f<\/span><span class=\"mspace\" style=\"margin-right:0.16666666666666666em;\"><\/span><span class=\"minner\"><span class=\"mopen delimcenter\" style=\"top:0em;\"><span class=\"delimsizing size3\">(<\/span><\/span><span class=\"mord text\"><span class=\"mord\">-<\/span><\/span><span class=\"mord\"><span class=\"mopen nulldelimiter\"><\/span><span class=\"mfrac\"><span class=\"vlist-t vlist-t2\"><span class=\"vlist-r\"><span class=\"vlist\" style=\"height:1.32144em;\"><span style=\"top:-2.314em;\"><span class=\"pstrut\" style=\"height:3em;\"><\/span><span class=\"mord\"><span class=\"mord\">3<\/span><\/span><\/span><span style=\"top:-3.23em;\"><span class=\"pstrut\" style=\"height:3em;\"><\/span><span class=\"frac-line\" style=\"border-bottom-width:0.04em;\"><\/span><\/span><span style=\"top:-3.677em;\"><span class=\"pstrut\" style=\"height:3em;\"><\/span><span class=\"mord\"><span class=\"mord\">4<\/span><\/span><\/span><\/span><span class=\"vlist-s\">\u200b<\/span><\/span><span class=\"vlist-r\"><span class=\"vlist\" style=\"height:0.686em;\"><span><\/span><\/span><\/span><\/span><\/span><span class=\"mclose nulldelimiter\"><\/span><\/span><span class=\"mclose delimcenter\" style=\"top:0em;\"><span class=\"delimsizing size3\">)<\/span><\/span><\/span><span class=\"mspace\" style=\"margin-right:0.2777777777777778em;\"><\/span><span class=\"mrel\">=<\/span><\/span><\/span><\/span>","formTextAfter":null,"answer":{"text":["4"]}}
{"type":"text","form":{"type":"math","options":{"comparison":"1","nofractofloat":false,"keypad":{"simple":true,"useShortLog":false,"variables":[],"constants":[]},"rendered":false},"text":"<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><\/span><\/span>"},"formTextBefore":"<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:1em;vertical-align:-0.25em;\"><\/span><span class=\"mord mathdefault\" style=\"margin-right:0.10764em;\">f<\/span><span class=\"mopen\">(<\/span><span class=\"mord\">2<\/span><span class=\"mord\">.<\/span><span class=\"mord\">1<\/span><span class=\"mclose\">)<\/span><span class=\"mspace\" style=\"margin-right:0.2777777777777778em;\"><\/span><span class=\"mrel\">=<\/span><\/span><\/span><\/span>","formTextAfter":null,"answer":{"text":["8.1"]}}
{"type":"text","form":{"type":"math","options":{"comparison":"1","nofractofloat":false,"keypad":{"simple":true,"useShortLog":false,"variables":[],"constants":[]},"rendered":false},"text":"<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><\/span><\/span>"},"formTextBefore":"<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:1em;vertical-align:-0.25em;\"><\/span><span class=\"mord mathdefault\" style=\"margin-right:0.10764em;\">f<\/span><span class=\"mopen\">(<\/span><span class=\"mord text\"><span class=\"mord\">-<\/span><\/span><span class=\"mord\">3<\/span><span class=\"mclose\">)<\/span><span class=\"mspace\" style=\"margin-right:0.2222222222222222em;\"><\/span><span class=\"mbin\">\u22c5<\/span><span class=\"mspace\" style=\"margin-right:0.2222222222222222em;\"><\/span><\/span><span class=\"base\"><span class=\"strut\" style=\"height:1em;vertical-align:-0.25em;\"><\/span><span class=\"mord mathdefault\" style=\"margin-right:0.10764em;\">f<\/span><span class=\"mopen\">(<\/span><span class=\"mord\">4<\/span><span class=\"mclose\">)<\/span><span class=\"mspace\" style=\"margin-right:0.2222222222222222em;\"><\/span><span class=\"mbin\">+<\/span><span class=\"mspace\" style=\"margin-right:0.2222222222222222em;\"><\/span><\/span><span class=\"base\"><span class=\"strut\" style=\"height:1em;vertical-align:-0.25em;\"><\/span><span class=\"mord mathdefault\" style=\"margin-right:0.10764em;\">f<\/span><span class=\"mopen\">(<\/span><span class=\"mord\">2<\/span><span class=\"mclose\">)<\/span><span class=\"mspace\" style=\"margin-right:0.2222222222222222em;\"><\/span><span class=\"mbin\">\u22c5<\/span><span class=\"mspace\" style=\"margin-right:0.2222222222222222em;\"><\/span><\/span><span class=\"base\"><span class=\"strut\" style=\"height:1em;vertical-align:-0.25em;\"><\/span><span class=\"mord mathdefault\" style=\"margin-right:0.10764em;\">f<\/span><span class=\"mopen\">(<\/span><span class=\"mord text\"><span class=\"mord\">-<\/span><\/span><span class=\"mord\">1<\/span><span class=\"mclose\">)<\/span><span class=\"mspace\" style=\"margin-right:0.2777777777777778em;\"><\/span><span class=\"mrel\">=<\/span><\/span><\/span><\/span>","formTextAfter":null,"answer":{"text":["-72"]}}
security
report
code
security
report
code
Before evaluating the function at x=- 43, we first need to identify which interval of the domain of the function - 43 belongs to. Since - 43 is about -1.33, it lies between -3 and 0. As such, the given input belongs to the second interval. f(x) = 2x-3, &if x ≤ -3 -3x, &if -3 < x ≤ 0 6, &if 0 < x ≤ 2 x+6, &if x > 2 Therefore, to evaluate the function at - 43 we will use the second expression, -3x.
As in the previous part, let's first determine the interval of the domain that includes the input 2.1. Because 2.1 > 2, it belongs to the last interval. f(x) = 2x-3, &if x ≤ -3 -3x, &if -3 < x ≤ 0 6, &if 0 < x ≤ 2 x+6, &if x > 2 Therefore, this time we will use the last expression of f(x), x+6.
We begin by noting that the given expression involves four different inputs, namely, -3, 4, 2, and -1. Therefore, to know which expression of the function we need to use for evaluating each input, let's locate them in the corresponding domain's intervals.
Having identified the expression we need to use for each input, we can substitute the inputs into their expressions and find the corresponding values. To do so, let's use a table of values!
| Input | Interval | Function | Evaluation |
|---|---|---|---|
| -3 | x ≤ -3 | f(x) = 2x-3 | f(-3) = 2(-3)-3 = -9 |
| 4 | x > 2 | f(x) = x+6 | f(4) = 4+6 = 10 |
| 2 | 0 < x ≤ 2 | f(x) = 6 | f(2) = 6 |
| -1 | -3 < x ≤ 0 | f(x) = -3x | f(-1) = -3(-1) = 3 |
Finally, let's substitute these values into the given expression and simplify.
security
report
code
The following graph represents the cost, in dollars, of buying x tickets to a magic show.
{"type":"text","form":{"type":"math","options":{"comparison":"1","nofractofloat":false,"keypad":{"simple":true,"useShortLog":false,"variables":[],"constants":[]},"rendered":false},"text":"<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><\/span><\/span>"},"formTextBefore":"<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.80556em;vertical-align:-0.05556em;\"><\/span><span class=\"mord\">$<\/span><\/span><\/span><\/span>","formTextAfter":null,"answer":{"text":["125"]}}
{"type":"choice","form":{"alts":["<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.64444em;vertical-align:0em;\"><\/span><span class=\"mord\">4<\/span><\/span><\/span><\/span> tickets","<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.64444em;vertical-align:0em;\"><\/span><span class=\"mord\">5<\/span><\/span><\/span><\/span> tickets"],"noSort":true},"formTextBefore":"","formTextAfter":"","answer":1}
{"type":"text","form":{"type":"math","options":{"comparison":"1","nofractofloat":false,"keypad":{"simple":true,"useShortLog":false,"variables":[],"constants":[]},"rendered":false},"text":"<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><\/span><\/span>"},"formTextBefore":null,"formTextAfter":"tickets","answer":{"text":["18"]}}
security
report
code
security
report
code
To determine the cost of buying 14 tickets, we need to determine the y-coordinate of the point for which x=14. To do so, let's draw the line x=14. Keep in mind that the point must lie on the graph of the given piecewise function.
We see that the line intersects the graph at the point (14,125). Therefore, buying 14 tickets has a cost of $125.
To determine whether it is cheaper to buy 4 or 5 tickets, let's start by finding the cost of buying 4 tickets. To do this, let's draw the line x=4.
Note that the point (4,50) belongs to the graph, while the point filled with white does not. Therefore, the cost of buying 4 tickets is $50. Now, let's draw the line x=5. It will be halfway between 4 and 6.
It can be seen that the line x=5 intersects the graph at a point whose y-coordinate is less than 50. This means that buying 5 tickets costs less than $50. Consequently, it is cheaper to buy 5 tickets than to buy 4 tickets.
To determine the maximum number of tickets that we can buy with $125, let's draw the line y=125.
We can see the line intersects the graph at two different points, (14,125) and (18,125). From this we can conclude that buying 14 tickets costs the same amount of money as buying 18 tickets. cc Number of Tickets & Cost [0.15cm] 14 & $125 18 & $125 Consequently, we can buy a maximum of 18 tickets with $125. In fact, note that we can also buy 17 tickets with $125 but we cannot buy 15 or 16 tickets for this price!
security
report
code
Consider the following piecewise function.
f(x)=⎩⎪⎪⎪⎪⎨⎪⎪⎪⎪⎧21x+5,-2.5,-2x+4,3x−13,if x<-3if -3≤x<0if 0≤x≤3if x>3
Which of the following is the graph of f(x)?
{"type":"choice","form":{"alts":["<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.7109375em;vertical-align:0em;\"><\/span><span class=\"mord text\"><span class=\"mord Roboto-Bold textbf\">A<\/span><\/span><\/span><\/span><\/span>","<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.7109375em;vertical-align:0em;\"><\/span><span class=\"mord text\"><span class=\"mord Roboto-Bold textbf\">B<\/span><\/span><\/span><\/span><\/span>","<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.73046875em;vertical-align:-0.009765625em;\"><\/span><span class=\"mord text\"><span class=\"mord Roboto-Bold textbf\">C<\/span><\/span><\/span><\/span><\/span>","<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.7109375em;vertical-align:0em;\"><\/span><span class=\"mord text\"><span class=\"mord Roboto-Bold textbf\">D<\/span><\/span><\/span><\/span><\/span>"],"noSort":true},"formTextBefore":"","formTextAfter":"","answer":2}
security
report
code
security
report
code
From the definition of f(x), we can see that the domain covers the entire number line — that is, the domain of the function is all the real numbers.
As we can see, the graph of f(x) does not have any horizontal gaps between the pieces. Knowing this, we can discard option D because it has a gap between x=3 and x=4.
On the other hand, note that the third domain of the function includes both endpoints, 0≤ x ≤ 3. Therefore, third piece of graph, from left to right, has to include both endpoints. Looking at the remaining three graphs, we can see that option A does not fulfill this condition, so we can discard option A.
As we can see, graphs B and C both have the correct distribution of the endpoints. Let's now take a look at each branch to check if they correspond to the function rule defined for each interval. For simplicity, let's start with the second piece of f(x), f(x)=-2.5. Note that in graph B, the second piece is graphed at y=-4. Therefore, we will also discard graph B.
Finally, let's verify that each part of graph C corresponds to the definition of f(x).
Consequently, the correct option is C.
security
report
code
Consider the following piecewise function.
g(x)={-⌊x⌋,⌊x⌋,if -5≤x<0if 0≤x<6
Which of the following is the graph of g(x)?
{"type":"choice","form":{"alts":["<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.7109375em;vertical-align:0em;\"><\/span><span class=\"mord text\"><span class=\"mord Roboto-Bold textbf\">A<\/span><\/span><\/span><\/span><\/span>","<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.7109375em;vertical-align:0em;\"><\/span><span class=\"mord text\"><span class=\"mord Roboto-Bold textbf\">B<\/span><\/span><\/span><\/span><\/span>","<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.73046875em;vertical-align:-0.009765625em;\"><\/span><span class=\"mord text\"><span class=\"mord Roboto-Bold textbf\">C<\/span><\/span><\/span><\/span><\/span>","<span class=\"katex\"><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"strut\" style=\"height:0.7109375em;vertical-align:0em;\"><\/span><span class=\"mord text\"><span class=\"mord Roboto-Bold textbf\">D<\/span><\/span><\/span><\/span><\/span>"],"noSort":true},"formTextBefore":"","formTextAfter":"","answer":1}
security
report
code
security
report
code
First, notice that both parts of g(x) involve the greatest integer function y=⌊ x ⌋, which is a step function. As such, both pieces of the graph of g(x) should look like a step function, similar to stairs. This leads us to discard graph C.
Note that the left-hand piece of graph A looks like a step function but the right-hand piece does not. Therefore, we can also discard graph A.
In contrast, graphs B and D both look like a step function on both branches of their graphs. Therefore, we need to make a deeper analysis. Note that both graphs are exactly the same for x≥ 0, which corresponds to the graph of y=⌊ x ⌋. However, for x< 0, the endpoints of some segments are different. Let's point out all the differences.
To determine which is the correct graph, we will test a point. For example, let's find g(-2). Since -2 < 0, we have to use the first part of g(x) to evaluate it. g(x) = -⌊ x ⌋ ⇓ g( -2) = -⌊ -2 ⌋ Since -2 is an integer, ⌊ -2 ⌋=-2. Let's substitute it into the right-hand side. g(-2) = -(-2) = 2 Consequently, the point (-2,2) belongs to the graph of g(x). We can see that graph B fulfills this condition, but graph D does not. The corresponding point on graph D is (-2,3). Therefore, we can discard graph D and conclude that the correct option is graph B.
Note that the left-hand piece is the graph of y=⌊ x ⌋ but, because of the minus sign in front of the function rule of the first interval, it is reflected in the x-axis.
security
report
code
Graphing Piecewise and Step Functions
Recommended exercises
To get personalized recommended exercises, please login first.
Loading content
Loading content