Question

Multiply these binomials.

(x - 9)(x + 9)

Answer 1

(x - 9)(x + 9)
= x(x + 9) -9(x + 9)
= x^2 +9x - 9x -81
=x^2 -81

Answer 2

you can use the formula of difference of two squares directly..

(a-b)(a+b) = a^2 - b^2