Question

Expand (3x+7)(3x-7) =

Answer 1

(3x + 7)(3x - 7) =

= 9x² + 21x - 21x - 49

= 9x² - 49

Answer 2

`9 {x}^(2) - 49`

Explanation:

Do FOIL, first outside inside last

3x × 3x = 9x^2

3x × -7 = -21x

7 × 3x = 21x

7 × -7 = -49

`9 {x}^(2) - 21x + 21x - 49 \: midde \: cancels \: each \: other \: out`

So it would just be 9x^2 - 49