Question

How do you multiply `(3f - 9) ( 3f + 9)`?

Answer 1

`"The answer is "9(f^2-9)`

Explanation:

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

`"let 3f=a" , "9=b`

`(3f)^2-9^2=9f^2-81`

`"or "9(f^2-9)`