ok so there's curve y=12x+3(x^2)-2(x^3)
the stationary points are (-1,-7) and (2,20)
i'm supposed to find the domain for which y has three real roots
the answer is -20<x<7, this is a typo right?
The answer -20<x<7 appears to correspond, possibly, to the question "What is the range for y corresponding to the domain that includes three real roots?" Then the answer given would be correct.