Question

Find the local minima, maxima and inflection points of:

a) f(x) = x^3-6x^2-135x
b) f(x) = x(pi) + cos(x)

Answer 1

a) to start off with a I would find f'(x), which is 3x^2-12x-135 and set it to 0 to solve for x. This is where i'm stuck. How do i solve for x?

Answer 2

3x^2-12x-135=0

you can divide both sides by 3 to simplify it a bit:
x^2 -4x -45 =0

solve using the quadratic formula
http://www.purplemath.com/modules/solvquad4.htm

or learn to factor
http://www.purplemath.com/modules/factquad.htm
(which you can do in some but not all circumstances)