The region bounded by the given curves is rotated about the specified axis. Find the volume of the resulting solid using any method.

y = x^2 + x - 2, y = 0, about the x-axis.

I'm lost on how to do this. The graph of x^2 + x - 2 would go under the graph and when you intersect that with y = 0, shouldn't you get a negative answer when you integrate it from root -1.61803 to 0.618034? But the book says the answer is 81pi/10.