How do you graph y=x|2x+5|?

1 Answer
Jan 19, 2018

Read below.

Explanation:

Let's think of it this way:
|a|=a and |a|=a

For our first case, we are just bringing out a outside the absolute value.
For the second case, we are finding the opposite of whatever was inside the absolute value sign.

So we can say that:
When 2x+50, then |2x+5|=2x+5
When 2x+5<0, then |2x+5|=2x5

Let's apply this to our function.
When 2x+50, then y=x(2x+5)y=2x2+5x
When 2x+5<0, then y=x(2x5)y=2x25x
We first garph these two parabolas:
desmos.comdesmos.com
Now, we ask ourselves,"For what values of x does 2x+50hold true?"
Similarly, "For what values of x does 2x+5<0 hold true?"

To find out the answer, we solve each inequality.
2x+50
2x5
x52

2x+5<0
2x<5
x<52

This is actually telling us that for any x values greater than or equal to 52, the blue parabola will apply. When x is smaller than 52, then the red parabola will apply. The green graph is the graph of our function.
So we now have:
Desmos.comDesmos.com

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