The volume of a solid revolution generated by rotating the curve y = f(x) and x = f(y) between x = a and x = b , y = a and y = b
through 360 degrees about the x-axis and y-axis is given and
The diagram shows the line y = 1, the line y = 4 and part of the curve . The shaded region is rotated through 360 degrees about the y-axis. Find the exact value of the volume of revolution obtained. Leave your answer in pi.