How do I find the minimum or maximum of this y = 2x³ + 3x² - 12x? It makes 2 curves.

Answer 1

y = 2x^3 + 3x^2 - 12x
y' = 6x^2 + 6x - 12 = 6(x+2)(x-1)

y'=0 when x=-2 or 1
Knowing what you do about cubic curves, you can see that

the local max occurs at x = -2, and
the local min is at x = 1

y(-2) = 20
y(1) = -7