I'm new in the forum.
I would like to know if my exercise is correct, often I make mistake in the calculation. If there is a way I can check my work.
Here is the question:
*Using the strategy to apply the First Derivative Test, classify the
left-hand stationary point:
X= -3 and x= 1
Step 1: the left stationery point of f is at x= -3;
Step 2: To classify the stationery point at x= -3, we choose test points xl= -4 and xr= -2, say. Then we have
f ’(xl)= f ’(-4) = 3(-4)(-1)(-5) = -60 < 0
f ’(xr)= f ’(-2) = 3(-2)(1)(-3) = 18 > 0
so f has a local minimum at x = -2, by the first derivative test.
I hope there is no mistake in that