81r^2-36rs+4s^2

Answer 1

I assume you want it factored.

Find two numerical factors for the two end terms that will add to get you the middle term.

9 * 9 or 27 * 3 or 81 * 1
2 * 2 or 4 * 1

(9 * 2) + (9 * 2) = 36

Now all you need to do is to pay attention to the negative sign.

(9r-2s)(9r-2s)