Question

How do you factor `-9r^2 + 81`?

Answer 1

`=-9(r-3)(r+3)`

Explanation:

The difference of squares rule states that: `a^2-b^2=(a-b)(a+b)`, and using this:

`-9r^2+81=-9(r^2-9)`
`=-9(r^2-3^2)`
`=-9(r-3)(r+3)`