Let f (x) = the third power of X - 6x square + 9x-3, and prove that f (x) has the maximum value when x = 1 and the minimum value when x = 3

Let f (x) = the third power of X - 6x square + 9x-3, and prove that f (x) has the maximum value when x = 1 and the minimum value when x = 3

F'(x)=3x^2-12x+9=3(x^2-4x+3)=0
x1=1,x2=3
x