Find the local minima, maxima and inflection points of:

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

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)

anonymous · Answer

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?

phi · Answer

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)