Question

For the question "Which binomial is a factor of 9x² – 64?

3x – 8
9x – 32
3x + 32
9x + 8

I got two different answers from the choices: (x + 8)(9x - 8).

What went wrong?

Answer 1

3x-8

Explanation:

9x²-64 is the same as

(3x)² - 8²

now we have the difference of 2 squares, a²-b² =(a -b)(a +b), where a=3x, b=8

9x²-64 = (3x-8)(3x+8)