For the first term of 9x2, we know 3*3 is 9 and x*x is x2. For the middle term, we need two numbers that add to zero and cancel out the middle term, but that multiply to -16.
9x2 - 0x - 16
since the middle is 0, it is cancelled
9x2 - 16
(3x - 4)(3x + 4)
CHECK:
9x2 + 12x - 12x - 16
adding +12 and -12 cancels out
9x2 - 16
ANSWER: (3x - 4)(3x + 4)
Hope this helps! :)
