1. The problem statement, all variables and given/known data Find the volume of 2sin(x) and -sin(x) from 0 to pi revolving around the y-axis 3. The attempt at a solution My problem is with the geometry of this problem, 2sin(x) is above the x-axis and -sin(x) is below the x-axis. My belief was that I should be adding on the extra area of -sin(x) because it lies below the x-axis. I don't understand why I should be subtracting in this case. Thanks edit: the axis of rotation is the y-axis. there are two parts, the first asks me to show, through differentiation, that the integral of x(sin(x))dx = sin(x) - x(cos(x)) + C. Done. For the second part they say use the result of part (a) to find the volume of the solid generated by revolving each plane region, the area between 2sin(x) and -sin(x), about the y-axis. I said x-axis, sorry my mistake.