Sketch the graph of y=(x+2)(X+1)(X-1) = X^3+2x^2-x-2 in the range -2.5< or equal to X < or equal to 1.5. (You must determine the points where the gradient is zero and where the curve crosses the x and y Axes.

I have substituted the values of x between the stated ranges to get my graph, I can then clearly see where the graph cross the x and Y axis.

I then have to find where the gradiet is zero, This is where my problem lies, I can see on the graph roughly where it will be, however i need the exact answer. All the books and example i have been able to find just show how to find the gradient at a specific point not a specific gradient.

I know that i haveto differentiate to get the gradient, but after that i am a little bit stuck.