Question

How do you find the product `(a-3)(a+3)`?

Answer 1

`(a-3)(a+3)=color(green)(a^2-9)`

Explanation:

Either remember the general case
`color(white)("XXX")(p-q)(p+q)=p^2-q^2` (sometimes called "the difference of squares")

...or do the multiplication
`(a-3)(a+3)`
`color(white)("XXX")=(a-3)a + (a-3)3` (using the distributive property)

`color(white)("XXX")=(a^2-3a)+(3a-9)`

`color(white)("XXX")=a^2-9`

(could also be done using FOIL or tabular multiplcation)