In general, the graph of the absolute value function
f (x) = a| x - h| + k
is a shape "V" with vertex (h, k).
To graph the absolute value function, we should be aware of the following terms.
Horizontal Shift :
Let us consider two different functions,
y = |x| and y = |x-1|
Vertex of the absolute value function y = |x| is (0, 0).
Vertex of the absolute value function y = |x-1| is (1, 0).
By comparing the above two graphs, the second graph is shifted 1 unit to the right. Since the value h is > 0, we have to move the graph h units to the right side.
Conclusion :
If h > 0, move the graph h units to the right.
If h < 0, move the graph h units to the left.
Vertical Shift :
Let us consider two different functions,
y = |x| and y = |x| + 1
Vertex of the absolute value function y = |x| is (0, 0).
Vertex of the absolute value function y = |x|+1 is (0, 1).
Instead of k, we have +1. So, we have to move the graph 1 unit up.
If the value of k is -1. We have to move the graph 1 unit down.
Conclusion :
If k > 0, move the graph k units up.
If k < 0, move the graph k units down.
Stretch and Compression :
Let us consider two different functions,
y = |x| + 3 and y = -|x|+3
Graph the following absolute value function.
Example 1 :
y = -|x + 2| + 11
Solution :
To graph, let us find the following.
By comparing the given absolute value function with
y = |x - h| + k
Vertex (h, k) :
(-2, 11)
Horizontal Translation :
h = -2
Move the graph two units to the left.
Vertical Translation :
k = 11
Move the graph 11 units up.
Stretches and Compressions :
a = -1
x-intercept :
Put y = 0.
0 = -|x + 2| + 11
-11 = -|x + 2|
|x + 2| = 11
(x + 2) = 11 and (x + 2) = -11
x = 9 and x = -13
y-intercept :
Put x = 0.
y = -|0 + 2| + 11
y = -2 + 11
y = 9
Example 2 :
y = |x| + 9
Solution :
To graph, let us find the following.
By comparing the given absolute value function with
y = |x - h| + k
Vertex (h, k) :
(0, 9)
Horizontal Translation :
h = 0
So, no horizontal shift.
Vertical Translation :
k = 9
Move the graph 9 units up.
Stretches and Compressions :
a = 1
x-intercept :
Put y = 0.
0 = |x| + 9
-9 = |x|
This will not happen, for any value of x we will not get the answer -9. So, it has no x-intercepts.
y-intercept :
Put x = 0.
y = |0| + 9
y = 9
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