Solve (x-6)(x+6) > 0: Finding Values Where Function is Positive

Question

Look at the following function:

y=(x6)(x+6) y=\left(x-6\right)\left(x+6\right)

Determine for which values of x x the following is true:

f(x) > 0

Step-by-Step Solution

To solve this problem, we need to find the values of x x that make (x6)(x+6)>0 (x-6)(x+6) > 0 .

Let's consider the critical points where each factor could change sign by setting each factor equal to zero:

  • x6=0 x-6 = 0 gives x=6 x = 6 .
  • x+6=0 x+6 = 0 gives x=6 x = -6 .

These critical points divide the number line into three intervals:

  • x<6 x < -6
  • 6<x<6 -6 < x < 6
  • x>6 x > 6

We will test each interval to see where f(x)=(x6)(x+6)>0 f(x) = (x-6)(x+6) > 0 :

1. Interval x<6 x < -6 :

If x<6 x < -6 , both (x6) (x-6) and (x+6) (x+6) are negative (e.g., test x=7 x = -7 ).
(x6)(x+6)=()()>0(x-6) \cdot (x+6) = (-)\cdot(-) > 0: The product is positive.

2. Interval 6<x<6 -6 < x < 6 :

If 6<x<6 -6 < x < 6 , (x6) (x-6) is negative, and (x+6) (x+6) is positive (e.g., test x=0 x = 0 ).
(x6)(x+6)=()(+)<0(x-6) \cdot (x+6) = (-)\cdot(+) < 0: The product is negative.

3. Interval x>6 x > 6 :

If x>6 x > 6 , both (x6) (x-6) and (x+6) (x+6) are positive (e.g., test x=7 x = 7 ).
(x6)(x+6)=(+)(+)>0(x-6) \cdot (x+6) = (+)\cdot(+) > 0: The product is positive.

Therefore, the inequality (x6)(x+6)>0 (x-6)(x+6) > 0 holds for x<6 x < -6 or x>6 x > 6 . Thus, the correct answer is:

x>6 x > 6 or x<6 x < -6

Answer

x > 6 or x < -6