algebra
posted by sam .
81r^236rs+4s^2

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.
(9r2s)(9r2s)