Question

What is the factorization of the expression below?

4x2 - 81

Answer 1

using the difference of squares:
\[(a^2-b^2) = (a+b)(a-b)\]
Think of \[4x^2 = 2x \times 2x\] and \[81 = 9 \times 9\]
If 4x^2=a^2 and 81=b^2, you get
a=2x and b=9
So, factored would be (2x+9)(2x-9)