2 2 s - r - 18*s + 81
s^2 - r^2 - 18*s + 81
1*(r + -9 + s)*(r + 9 - s)
(1*(r - (9 + s)))*(r + (9 - s))
81.0 + s^2 - r^2 - 18.0*s
-(-9 + r + s)*(9 + r - s)