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| | 12 Theory slides |
| | 8 Exercises - Grade E - A |
| | Each lesson is meant to take 1-2 classroom sessions |
Jordan is getting ready for the inter-class swimming competition at her school.
She swims to the far end of the pool and comes back to the starting point. The function below models Jordan's distance from the far end of the pool after t seconds. d(t) = 2|t-25|
Examine the given piecewise functions and inequalities on the left. Match them with their corresponding graph.
An expression involving an absolute value can be defined as follows. |a| = - a, & if a<0 a, & if a≥0 Using this definition, an absolute value function can be written as a piecewise function. Consider an example function. f(x) = - 4|1/2x+1 |+5 The above function will be rewritten as a piecewise function. The procedure can be completed in two steps.
(II): Distribute -1
(I), (II):Distribute - 4
(I), (II): Add terms
Finally, the inequalities describing the domains of the pieces will be rearranged. To do so, subtract 1 from both sides of the inequalities, then multiply both sides by 2. f(x)= 2x+9, & if x<- 2 - 2x+1, & if x ≥ - 2 The given absolute value function has been written as a piecewise function.
| Absolute Value Function | Piecewise Function |
|---|---|
| f(x) = - 4|1/2+1 |+5 | f(x) = 2x+9, & if x<- 2 - 2x+1, & if x ≥ - 2 |
Dylan and Kriz have been asked to write the following absolute value function as a piecewise function. f(x)=- 7|7-x|+8 The functions they wrote are shown in the diagram.
Who correctly wrote the given function as a piecewise function?
(I): Distribute -1
(I), (II):Distribute - 7
(I), (II): Add terms
Finally, the domain of this piecewise function should be rearranged. First, 7 will be subtracted from both sides of the inequalities. f(x)= - 7x+57 & if 7-x < 0 7x-41 & if 7-x ≥ 0 ⇕ f(x)= - 7x+57 & if - x < - 7 7x-41 & if - x ≥ - 7 By dividing the inequalities by - 1, the parts of the domain can be identified. Recall that dividing an inequality by a negative number reverses the inequality symbol. f(x)= - 7x+57 & if - x < - 7 7x-41 & if - x ≥ - 7 ⇕ f(x)= - 7x+57 & if x > 7 7x-41 & if x ≤ 7 The absolute value function is now completely rewritten as a piecewise function.
| Absolute Value Function | Piecewise Function |
|---|---|
| f(x)=- 7 |7-x|+8 | f(x) = - 7x+57 & if x > 7 7x-41 & if x ≤ 7 |
Comparing this function with the functions written by Dylan and Kriz, it appears that Kriz wrote it correctly.
Absolute value functions can be written as piecewise functions. By graphing the pieces for their domains, the graph of the absolute value function can be obtained. As an example, the following function will be graphed. f(x) = |2x-6|-2 Its graph can be drawn in four steps.
LaShay likes to make connections between the shapes she finds in daily life and the concepts she encounters in her math lessons. While watching a documentary about swallows, LaShay thinks that the wings of a swallow can be modeled by an absolute value function.
f(x) = - 0.6x+2.4 & if 0 ≤ x < 4 0.6x-2.4 & if 4 ≤ x ≤ 8
The point (8,2.4) is on the graph. Using these three points, two function rules can be written. One for the decreasing part, and the other for the increasing part of the graph. The domain of these parts can be written as follows. Decreasing Part:& 0 ≤ x < 4 Increasing Part:& 4 ≤ x ≤ 8 Note the point at x=4 can belong to either piece, so long as it belongs to only one of them. The next step will then be to find the equation for both lines. For this, recall the slope-intercept form of a linear function. y= mx + b In this form m is the slope of the line and b is the y-intercept. Start with the decreasing part. The y-intercept and slope can be found from the graph.
For this line the y-intercept is b= 2.4 and the slope is m= - 0.6. Decreasing Part & Domain y= - 0.6 x + 2.4 & 0 ≤ x < 4 Similarly, an equation for the increasing part can also be written.
For the increasing line, the y-intercept is - 2.4 and the slope is 0.6. Increasing Part & Domain y= 0.6 x - 2.4 & 4 ≤ x ≤ 8 Knowing the equations for both lines, the absolute value function can be written as a piecewise function. f(x)= - 0.6x+2.4 & if 0 ≤ x < 4 0.6x-2.4 & if 4 ≤ x ≤ 8
f(x)= - 0.6x+2.4 & if 0 ≤ x < 4 0.6x-2.4 & if 4 ≤ x ≤ 8 To do so, the function rules can be rearranged so that one rule contains an expression and the other rule contains its opposite.
(I), (II): Factor out 0.6
(I): Factor out - 1
The function rules contain the expressions - (x-4) and x-4. These expressions produce non-negative values in their domains. Therefore, they can be written using absolute values. f(x)= - 0.6(x-4) & if 0 ≤ x < 4 0.6(x-4) & if 4 ≤ x ≤ 8 ⇓ f(x) = 0.6|x-4| The domain of this absolute value function is the union of the domains for the function rules. Function: & f(x) = 0.6|x-4| Domain: & 0 ≤ x ≤ 8
The Rio Negro Bridge is a 3595-meter long cable-stayed bridge over the Rio Negro in Brazil.
h(x) = - 0.6x+2.4 & if 0 ≤ x < 4 0.6x-2.4 & if 4 ≤ x ≤ 8
Graph:
h(x) = - 0.6 |x-200|+120 ⇕ h(x) = - 0.6( - [x-200])+120 & if x < 200 - 0.6( x-200)+120 & if x ≥ 200 The function rules can be simplified.
(I): Distribute -1
(I), (II): Distribute - 0.6
(I), (II): Add terms
Next, each function rule will be drawn separately and their graphs will be combined. First draw the graph of y=0.6x.
The graph ends with an open circle because its domain is the set of x-values less than 200. For x-values greater than or equal to 200, the graph of y=- 0.6x+240 will be drawn. This is a linear function written in slope-intercept form. y = - 0.6x + 240 ⇓ l Slope: - 0.6 y-intercept: 240 Using this information, its graph can be drawn.
This piece ends with a closed circle, as 200 is in its domain. Finally, both graphs will be combined on the same coordinate plane.
Since all the measures are in meters, the distance between these two points is 400 meters.
An absolute value inequality can be formed by replacing the equals sign in an absolute value function with an inequality symbol. Therefore, writing an absolute value inequality as a piecewise inequality can be compared to writing an absolute value function as a piecewise function. Consider an example absolute value inequality. g(x) > 3|2x-7 |-9 This inequality can be rewritten as a piecewise inequality in two steps.
(II): Distribute - 1
(I), (II): Distribute 3
(I), (II): Subtract terms
Finally, the inequalities used to describe the parts of the domain will be rearranged. To do so, add 7 to both sides and then divide both sides by 2. g(x) > 6x-30 & if 2x-7 ≥ 0 [0.6em] - 6x+12 & if 2x-7 < 0 ⇕ g(x) > 6x-30 & if x ≥ 72 [0.6em] - 6x+12 & if x< 72 The given absolute value inequality has been written as a piecewise inequality.
Absolute value inequalities in two variables can be written as piecewise inequalities. By drawing the graph of each piece in the piecewise inequality, the graph of the absolute value inequality is also drawn. Consider an absolute value inequality. g(x) < - 0.5|x+6|+2 This inequality can be graphed as a piecewise inequality in four steps.
(I): Distribute -1
(I), (II):Distribute - 0.5
(I), (II): Add terms
Now, the inequalities describing the domain of the pieces will be rearranged. To do so, subtract 6 from both sides of the inequalities. g(x) < 0.5x+5 & if x<- 6 - 0.5x-1 & if x ≥ - 6 To graph the piecewise-defined inequality, first each individual piece of the inequality will be drawn. Then the graphs will be combined on the same coordinate plane.
The domain for the boundary line contains x-values less than - 6. This means that the only part of the graph that should be considered is to the left of x = - 6. Additionally, the boundary line will have an open endpoint at x=- 6.
Next, the region to be shaded will be determined. To do so, choose a point whose x-coordinate is less than - 6 but is not on the boundary line — for example, (- 8,0).
Since the point satisfies the inequality, the region that contains the point will be shaded.
The domain for the boundary line contains the x-values greater than or equal to - 6. This means that the only part of the graph that should be considered is to the right of x = - 6. Additionally, the boundary line will have a closed endpoint at x=- 6.
Now, to determine which region must be shaded choose a point with a x-coordinate greater than - 6 but that is not on the line. For example, (0,0) can be used.
Since the point does not satisfy the inequality, the region that does not contain the point will be shaded.
Maya notices that the region illuminated by a car's left headlight can be modeled by an absolute value inequality.
The inequality below models this region. g(x) ≥ 5|x-0.5| - 1.5
g(x - 1) ≥ 5|x - 1-0.5| - 1.5 ⇓ y ≥ 5|x-1.5| - 1.5 Considering the definition of absolute values, this inequality can be divided into two pieces. y ≥ 5 |x-1.5| - 1.5 ⇓ y ≥ - 5 [ - (x - 1.5)] - 1.5 & if x - 1.5 < 0 5( x - 1.5) - 1.5 & if x - 1.5 ≥ 0 The expressions can be simplified.
(I): Distribute -1
(I), (II):Distribute 5
(I), (II): Subtract terms
Now, the inequalities describing the domains of the pieces will be rearranged. To do so, 1.5 will be added to both sides of the inequalities. y ≥ - 5x+6 & if x<1.5 5x-9 & if x≥ 1.5
The boundary line is in slope-intercept form. Its graph can be drawn by using the slope and y-intercept. Since the inequality is not strict, the boundary line will be solid. Additionally, since x is less than 1.5, the boundary line will have an open endpoint at x=1.5.
To determine the region to be shaded, choose a test point and substitute it into the inequality — for example, (0,0).
Since the point does not satisfy the inequality, the region that does not contain the test point will be shaded. Note that only points in the corresponding domain x<1.5 will be considered.
Next, the second piece of the inequality will be graphed.
The boundary line's slope is 5. Also, (1.5,- 1.5) satisfies the second piece. This point is the leftmost point of the boundary line because its domain is x≥ 1.5. Additionally, since the inequality is non-strict, the boundary line will be solid.
Now, choose a point not on the boundary line whose x-coordinate is greater than or equal to 1.5 — for example, (4,0).
Since the point did not satisfy the inequality, the region that does not contain the point that will be shaded.
Finally, the graphs of the two pieces can be combined on the same coordinate plane.
Maya can now complete her image.
Considering the methods and examples discussed in this lesson, the challenge presented at the start can now be solved. Jordan swims to the far end of the pool and comes back to the starting point. The absolute value function that models Jordan's distance from the far end after t seconds is given.
Domain: 0≤ t ≤ 50
Range: 0≤ d(t) ≤ 50
d(t)= 2|t-25| The absolute value expression in this function can be divided into two cases.
With this information in mind, the absolute value function can be written as a piecewise function. d(t) = 2 [ - (t-25)] & if t-25 < 0 2 ( t-25) & if t-25 ≥ 0 Next, the function rules need to be simplified.
The inequalities can be solved for t. To do so, 25 will be added to both sides of the inequalities. d(t) = - 2t+50 & if t-25 < 0 2t-50 & if t-25 ≥ 0 ⇕ d(t) = - 2t+50 & if t<25 2t-50 & if t≥ 25
d(t) = - 2t+50 & if t<25 2t-50 & if t≥ 25 First graph y=- 2t +50. This function has a slope of - 2 and a y-intercept of 50. Since the domain for this piece is the set of numbers less than 25, the graph should end with an open point at t=25.
Similarly, the other piece y=2t-50 can be drawn. Its slope is 2. The domain of this piece contains the t-values greater than or equal to 25. Therefore, it has a closed endpoint at t=25.
The combination of the above graphs is the graph of the piecewise function.
Since t represents time and d(t) represents distance, they cannot be negative. Therefore, both t and d(t) are non-negative numbers. t & ≥ 0 d(t) & ≥ 0 Recall that Jordan swims to the far end of the pool and comes back to the starting point. At t=0, Jordan is at the starting point. Therefore, by substituting t=0 into the given function the length of the pool can be found.
At t=0, Jordan is 50 meters away from the end. With this information it can be said that d(t)≤ 50. When Jordan is back to the starting point, she is again 50 meters away from the far end. Therefore, to calculate how many seconds it takes her to swim to the far end and come back to the starting point, d(t)=50 will be substituted in the given function.
d(t)= 50
.LHS /2.=.RHS /2.
Rearrange equation
State solutions
(I), (II): LHS+25=RHS+25
Jordan is 50 meters away from the far end at t=0 and t=50. Therefore, it takes her 50 seconds to swim to the far end and come back to the starting point. With this information it can be said that t≤ 50, so the domain and the range can be written. Domain: & 0 ≤ t ≤ 50 Range:& 0 ≤ d(t) ≤ 50 This means that only the first quadrant is relevant.
We need to write the given absolute value equation as a piecewise function. y = - 4|x-7| We can rewrite the expression |x-7| by using the definition of an absolute value. If x-7 is less than 0, its absolute value is equal to its opposite value. Conversely, if x-7 is greater than or equal to 0, its absolute value is equal to itself. |x-7| = - (x-7) & if x-7 < 0 x-7 & if x-7 ≥ 0 Considering this definition, we can rewrite the given function. y = - 4 [ - (x-7)] & if x-7 < 0 - 4 ( x-7) & if x-7 ≥ 0 Now we simplify each function rule.
Finally, we solve the inequalities describing the domain of each piece. To do so, we need to add 7 to both sides of the inequalities. y= 4x-28 & if x < 7 - 4x+28 & if x ≥ 7 This corresponds to option A.
Again, we need to write the absolute value function y= 5|x-8|+3 as a piecewise function. Let's start by recalling how to write the vertex form of an absolute value function, g(x)= a|x- h|+ k, as a piecewise function.
g(x) =
a[-(x- h)]+ k, if x- h < 0
a(x- h)+ k, if x- h ≥ 0
Using this, let's identify the values for our function.
g(x) = & a|x- h|+ k
& ⇓
y = & 5|x- 8|+ 3
Now, we will substitute a= 5, h= 8, and k= 3 into the above piecewise function.
We need to solve the inequalities describing the domain of each piece. y= - 5x+43, & if x< 8 5x-37, & if x ≥ 8 This corresponds to option C.
We need to write the given absolute value equation as a piecewise function. y = |3x+6|+4 We can rewrite the expression |3x+6| by using the definition of an absolute value. If 3x+6 is less than 0, its absolute value is equal to its opposite value. Conversely, if 3x+6 is greater than or equal to 0, its absolute value is equal to itself. |3x+6| = - (3x+6) & if 3x+6 < 0 3x+6 & if 3x+6 ≥ 0 Considering this definition, we can rewrite the given equation.
Finally, we solve the inequalities describing the domain of each piece. To do so, we need to subtract 6 from both sides and then divide each side by 3. y= - 3x-2 & if x < - 2 3x+10 & if x ≥ - 2 The resulting piecewise function corresponds to option B.
Let's use the piecewise function found in the previous part to graph the given function. We will draw each function rule separately and then combine them.
y=
- 3x-2 & if x < - 2
3x+10 & if x ≥ - 2
First, we will draw the graph of y=- 3x-2.
y = - 3x - 2 ⇒ l Slope: - 3 y-intercept: - 2
Note that the domain for this piece is x < - 2. Let's draw it.
The graph ends with an open circle because its domain is the set of x-values less than - 2. For x-values greater than or equal to - 2, we will draw the graph of y=3x+10. y = 3x + 10 ⇒ l Slope: 3 y-intercept: 10 Let's draw it.
This piece starts with a closed circle, as - 2 is in its domain. Finally, we combine the graphs on the same coordinate plane.
Therefore, the answer is option A.
Dylan writes the function y = - |- 13x+1 |-1 as a piecewise function and then graphs each piece as shown in the diagram.
Which of the following sentences corrects the mistakes made? I. & The domain of the first function rule & should be x > 3. II. & The endpoint of Piece II should be closed. III. & The domain of the second function rule & should be x ≤ 3. IV. & The endpoint of Piece I should be closed.
Let's first write the given absolute value function as a piecewise function. Then, we will identify the error in the presented work. y = - |- 1/3x+1 |-1 We can rewrite the expression | - 13x+1 |. If - 13x+1 is less than 0, its absolute value is equal to its opposite value. Conversely, if - 13x+1 is greater than or equal to 0, its absolute value is equal to itself. |- 1/3x+1 |= - (- 13x+1 ) & if - 13x+1 < 0 [0.5em] - 13x+1 & if - 13x+1 ≥ 0 Considering this definition, we can write a piecewise function.
Finally, we solve the inequalities. To do so, we need to subtract 1 from both sides of the inequalities and multiply by - 3. Note that multiplying by a negative number flip the inequality symbol. y= - 13x & if - 13x+1 < 0 [0.5em] 13x-2 & if - 13x+1 ≥ 0 ⇓ y= - 13x & if x > 3 [0.5em] 13x-2 & if x ≤ 3 Comparing the resulting function with the one Dylan wrote, we see that the inequality symbols were not flipped. Therefore, Statements I and III apply in this case. Analyzing each of those statements, let's consider the characteristics of their graphs, respectively.
| Statement | Graph |
|---|---|
| Statement I: The domain for the first piece is x > 3. | Because of the strict inequality symbol, its endpoint should be open. |
| Statement III: The domain for the second piece is x ≤ 3. | Because of the non-strict inequality symbol, its endpoint should be closed. |
We can use this information to now draw their graphs.
Notice that the graph of Piece II ends with a closed circle. Therefore, Statement II also corrects Dylan's mistake. As a result, we will choose the first three statements, I, II and III.
The graph of an absolute value function is shown.
Which piecewise function corresponds to the graph?
We are given the graph of an absolute value function.
As we can see, the behavior of the absolute value function changes at the vertex. Therefore, this is a good point to separate the graph into two pieces, both being straight lines. Our next step will be to find the equation for both lines. For this, let's recall the slope-intercept form of a line. y=mx + b In this form, m is the slope of the line and b is the y-intercept. We can start with the line to the left of the vertex first. We can identify the slope from the given graph.
For this line, the slope is m=5. We can substitute a point on the graph to find the y-intercept. Let's use (- 7,- 3).
Therefore, the equation for the left-hand part is y=5x+32. We will now do the same with the line to the right of the vertex.
Then, for this second line, the slope is m=- 5. To find the y-intercept, we can substitute (- 5,- 3).
Therefore, the equation for the right-hand part is y=- 5x-28. Knowing the equations for both lines allows us to write the absolute value function as the combination of two functions. y= 5x+32 - 5x-28 Last, let's decide the domain of each piece. The pieces meet and change directions at x=- 6, so this is where our domain needs to change. The point at x=- 6 can belong to either piece, as long as it belongs to only one of them. This means that we can correctly write the piecewise function in two different ways. y= 5x+32, & if & x ≤ - 6 - 5x-28, & if & x > - 6 or y= 5x+32, & if & x < - 6 - 5x-28, & if & x ≥ - 6 Therefore, the correct answer is option C.
We have been given a graph that shows the path of sunlight as it reflects off the water.
To write this as an absolute value function, the point of reflection is going to be the vertex. Recall the vertex form of an absolute value function. f(x)=a|x- h|+ k Here, the point ( h, k) is the vertex. Let's substitute our vertex ( 5, 0) into this equation. f(x)=a|x- 5|+ 0 ⇓ f(x)=a|x-5| Now we can solve for a by substituting another known point into the equation. Let's use ( 4, 2).
We can now write our final equation. f(x)=2|x-5| Note that the absolute value function can also be written as f(x)=|2x-10|.
To write the absolute value function as a piecewise function, we first need to determine where the function changes its direction because this is where our domains will split. In this case, this occurs when x=5.
We will let the domain of the left piece be all real numbers less than 5. Domain Left Piece: x < 5 The right piece of the function will then have a domain that includes all real numbers greater than or equal to 5. Domain Right Piece: x ≥ 5 Next, we can write the function as two separate equations by splitting our absolute value into its two cases: one positive and one negative. f(x)= 2[-(x-5)], & x < 5 2(x-5), & x ≥ 5 We can simplify these equations a little bit. Let's start with the negative case.
Now we can simplify the positive case. f(x)=2(x-5) ⇓ f(x)=2x-10 Finally, we can write the rule of the piecewise function. f(x)= -2x+10, & if x< 5 2x-10, & if x≥ 5 Therefore, the correct answer is option A.