Question

Can someone explain me how to do this STEP BY STEP ?

Answer 1

In order to find the turning point, you need to find the rate of change of the slope.

At the turning point, the slope will be 0.

So, you should take the derivative of T(x): 

T(x)' = 3(x+5)^2, you will see only when x = -5, T(x)' = 0

So when x < -5, T(x)' >0, and x>-5, T(x)' > 0 as well

Therefore, the turning point is unique: x= -5