Question

How do you multiply `(9-w)(9+w)`?

Answer 1

`81-w^2`

Explanation:

This is something you must keep in mind: for every `a` we have

`(a-w)(a+w)=a^2- aw + aw-w^2=a^2-w^2`

In this case `a=9` so `(9-w)(9+w)=9^2-w^2=81-w^2`