Find the stationary points of this function f x -x 3 plus 9x 2-15x-10?

f(x) = -x3 + 9x2 - 15x - 10

=> df/dx = -3x2 + 18x - 15 = -3*(x - 1)*(x - 5)

df/dx = 0 => x = 1 or x = 5

So, the stationary points are x = 1 and x = 5