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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|
First, identify the expression that involves absolute value. f(x) = - 4 |1/2x+1 | +5 This expression is equivalent to - ( 12x+1) if 12x+1 is less than 0. Conversely, this expression is equivalent to 12x+1 if 12x+1 is greater than or equal to 0. |1/2x+1|= - ( 12x+1 ), & if 12x+1<0 [0.6em] 12x+1, & if 12x+1 ≥ 0 Now this piecewise definition of the absolute value expression can be used for the given function. f(x) = - 4 ( - ( 12x+1 ) ) + 5, & if 12x + 1 < 0 [0.6em] - 4 ( 12x+1 ) + 5, & if 12x + 1 ≥ 0
(II): Distribute -1
(I), (II):Distribute - 4
(I), (II): Add terms
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.
Start by identifying the absolute value expression.
(I): Distribute -1
(I), (II):Distribute - 7
(I), (II): Add terms
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.
By the definition of absolute value, an absolute value expression can be divided into two. With this in mind, two function rules for the given absolute value function can be defined. f(x) = |2x-6|-2 ⇕ f(x) = - (2x-6)-2 & if 2x-6<0 2x-6-2 & if 2x-6 ≥ 0 After simplifying the expressions and inequalities, a piecewise-defined function is obtained. f(x) = - 2x+4 & if x< 3 2x-8 & if x ≥ 3 To graph the function, each individual piece will be graphed and then combined on the same coordinate plane.
First the graph of y=- 2x+4 will be drawn for the domain x<3. Notice that this piece is written in slope-intercept form. y= - 2x+ 4 This function has a slope of - 2 and a y-intercept of 4. Since the domain of this piece domain does not contain 3, its graph ends with an open point at x=3.
Now, the other piece will be drawn for the domain x ≥ 3. y= 2x - 8 Using its slope 2 and y-intercept - 8, the graph of the second piece can be drawn. Since this time 3 belongs to the domain, the graph of this piece ends with a closed point at x=3.
Finally, these two pieces can be combined on the same coordinate plane.
f(x) = - 0.6x+2.4 & if 0 ≤ x < 4 0.6x-2.4 & if 4 ≤ x ≤ 8
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
(I), (II): Factor out 0.6
(I): Factor out - 1
h(x) = - 0.6x+2.4 & if 0 ≤ x < 4 0.6x-2.4 & if 4 ≤ x ≤ 8
Graph:
(I): Distribute -1
(I), (II): Distribute - 0.6
(I), (II): Add terms
Since all the measures are in meters, the distance between these two points is 400 meters.
First, identify the expression that involves the absolute value. g(x) > 3 |2x-7|-9 If 2x-7 is greater than or equal to 0, then its absolute value is equal to itself. Conversely, if 2x-7 is less than 0, then its absolute value is equal to its opposite value. |2x - 7| = 2x - 7 & if 2x - 7 ≥ 0 - (2x - 7) & if 2x - 7 < 0 Now, the piecewise definition of the absolute value expression can be used for the given inequality. g(x) > 3 (2x - 7) - 9 & if 2x - 7 ≥ 0 3 [ - (2x - 7)] - 9 & if 2x - 7 < 0
(II): Distribute - 1
(I), (II): Distribute 3
(I), (II): Subtract terms
(I): Distribute -1
(I), (II):Distribute - 0.5
(I), (II): Add terms
Begin by determining the boundary line. This line can be found by replacing the inequality symbol with the equals sign. First Piece & Boundary Line y < 0.5x+5 & y = 0.5x+5 The boundary line is already written in slope-intercept form. Using the slope and y-intercept, the line can be graphed. Since the inequality is strict, the line will be dashed.
The second piece can be graphed similarly. First, write the equation of the boundary line. Second Piece & Boundary Line y < - 0.5x-1 & y= - 0.5x-1 The slope and the y-intercept of the boundary line are - 0.5 and - 1, respectively. Since the inequality is strict, the boundary line will be dashed.
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
(I): Distribute -1
(I), (II):Distribute 5
(I), (II): Subtract terms
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.
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.
d(t)= 50
.LHS /2.=.RHS /2.
Rearrange equation
State solutions
(I), (II): LHS+25=RHS+25
For each absolute value function given, select the piecewise function that represents it.
y = - 4|x - 7|
y = 5|x - 8|+3
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.
Which of the following piecewise functions corresponds to the absolute value function y = |3x+6|+4?
Which of the following is the graph of the given absolute value function?
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.
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.
Tadeo and Zain go fishing at a local lake. They bet sunburned by being hit with direct sunlight as well as the sunlight that is reflected off the water. The diagram shows the path of sunlight reflecting off the water.
Which of the following piecewise functions represents the function written in the previous part?
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.