Question

The local minimum of the cubic function:
y= -1/3x^3 + 6x^2 - 27x - 9
is found when x=?

Answer 1

-x^2 + 12x - 27 = 0
-x^2+12x = 27
-x^2+x = 27/-12
x=-2.25

Answer 2

correct or wrong?

Answer 3

-x^2+12x = 27
x^2-12x+27=0
this is the quadratic equation you need to solve, you will get 2 roots of x.