Big Ideas Math Algebra 1, 2015
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Big Ideas Math Algebra 1, 2015 View details
7. Graphing Absolute Value Functions
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Exercise 7 Page 159

Practice makes perfect
a We are given the following absolute value equation.

g(x)=|- 12x+2|+1 This is a transformation of the parent function y=|x|. To see how each of the parameters is affecting the parent function, it will be helpful to rewrite it first. g(x)=|- 12x+2|+1 ⇕ g(x)=|- 12 ( x-4)|+1This way we can look at each of the transformations individually. Notice that there is no general recipe for how to obtain a function from its parent function by transformations. However, there are a couple good things to remember.

  • Usually, we want to look at horizontal transformations before any vertical transformations.
  • Begin with the reflections.

First, we can do a reflection in the y-axis. This will transform the graph of the parent function, y=|x|, to the graph of y=|- x|. Notice that, since the graph of y=|x| is symmetrical about y-axis, this will not change how it looks.

Now, let's do a horizontal translation 4 units to the right. Then the graph of y=|- x| becomes y=|-(x-4)|.

Next, we will do a vertical shrink by a factor of 2. This transforms the graph of y=|-(x-4)| to the graph of y= 12|-(x-4)| ⇔ y=|- 12(x-4)|.

Finally, we have a vertical translation 1 unit up. From y=|- 12(x-4)| we get the final graph, y=|- 12(x-4)|+1.

Notice that there are many ways to obtain the graph of our function transforming the graph of its parent function. Here we considered only one of the many possibilities.

b To graph the function without going through the entire process of transforming the parent function, we can make a table of values. Then we only need to plot the ordered pairs that we find.
x |-1/2x+2|+1 Simplify g(x)
-4 |-1/2( -4)+2|+1 |4|+1 5
-2 |-1/2( -2)+2|+1 |3|+1 4
0 |-1/2( 0)+2|+1 |2|+1 3
2 |-1/2( 2)+2|+1 |1|+1 2
4 |-1/2( 4)+2|+1 |0|+1 1
6 |-1/2( 6)+2|+1 |-1|+1 2

Now we can plot these points and connect them to create our graph of g(x).