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

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Answer 1 · 2017-04-17T22:54:35

$81-w^2$

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 $(9-w)(9+w)=9^2-w^2=81-w^2$

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