2 9*x - 81
9*x^2 - 1*81
1*(x + 3)*(x - 3)
(1*(x + 3))*(x - 3)
-81.0 + 9.0*x^2
/ 2\ 9*\-9 + x /
9*(-9 + x^2)
9*(-3 + x)*(3 + x)