2 4*x - 36
4*x^2 - 1*36
1*(x + 3)*(x - 3)
(1*(x + 3))*(x - 3)
-36.0 + 4.0*x^2
4*(-3 + x)*(3 + x)
/ 2\ 4*\-9 + x /
4*(-9 + x^2)