My problem is that whenever I have to use cubic functions - whether it's finding the roots (when dy/dx kis a cubic function) or finding the x-intercepts... With quadratic functions I usually use the quadratic formula. I try to figure out how to factor these equations in my head but I can rarely get it right.
Right now my problem is with finding the x-intercepts of
y = 2x3 - 3x2 - 12x
Finding the local maximum/minimum when dy/dx = 4x3 + 12x2 - 4x - 12
The Attempt at a Solution
I've tried using newton's method on the relevant equation question, but that failed. x1 equalled -3 and x2 equalled 109, using an initial guess of 1. I won't put working because I think this really isn't what I'm supposed to do.
Don't really need answers to these questions, just really need some help on how to deal with cubic functions. Thanks a lot if anyone can help.