f(x)= - 2x^3 + 45x^2 -300x +9

Question

There are 3 intervals (-inf,A], [A,B], [B, inf) where A and B are critical points.

Find A and B?
For each of the intervals is it decreasing or increasing??

I found the derivative which is -6x^2+90x-300
-6(x^2-15x +50)
(x-5)(x-10) so I thought the critical points would be 5 and 10 but that's not what my book says??

Answer 1

Nevermind I got it!