Question

How to solve (x+7)(x-9)>0

Answer 1

x < -7, x > 9.

Explanation:

Solve for x.

x = -7, 9

From the values of x above, we have these 3 intervals to test.

`x < - 7`

`- 7 <x < 9`

`x > 9`

Pick a test point for each interval.

For the interval x < −7:

Let's pick x=−8. Then, (-8 + 7) (-8 - 9) > 0.

After simplifying, we get 17>0, which is true

Keep this interval.

Let's pick x=0. Then, (0+7)(0-9) > 0.

After simplifying, we get −63 > 0, which is false.

Drop this interval.

For the interval x > 9:

Let's pick x=10. Then, (10+7)(10-9)>0.

After simplifying, we get 17 > 0, which is true

Keep this interval.

Therefor, the answer is x < -7, x > 9.