# Thread: Help with turning points

1. ## Help with turning points

have to admit this is not my strongest module.

locate the turning points of the function y = xcubed - 27x +12 and determine their nature.

i know i need to differtating to obtain the dervied function.

but i need to be shown how and why, beacuse would like to get more knowledge on this

any help on this question would be great. going step by step wuld help me

thank you

2. $\displaystyle f'(x)=3x^2-27=0\Leftrightarrow x=3\;\vee\; x=-3$

Now study the sign of $\displaystyle f'(x)=3(x-3)(x+3)$ in $\displaystyle \mathbb{R}$ .