Question

Write as a polynomial:

2(x–3)(x+3)

Answer 1

Long way:

2(x-3)(x+3) = 2(x*x + 3*x - 3*x - 3*3)

2(x-3)(x+3) = 2(x^2 - 9)

2(x-3)(x+3) = 2x^2 - 2*9

2(x-3)(x+3) = 2x^2 - 18

Shortcut way:

Using formula (x+a)(x-a) = x^2 - a^2, where a = 3, in the case of (x+3)(x-3), so we have

(x+3)(x-3) = x^2 - 9.

Then, we multiply that by 2, which gives 2x^2 - 18.