Step 3 Therefore the volume of the solid of revolution about the y axis is 243x Exercise b the x axis Step 1 To find the volume of a solid of revolution about the x axis use the horizontal Traver Step 2 Volume V x 50 40 According to the Washer method Volume V V R x rex dx 20 The representative rectangle is shown in the figure The outer and inner radii of this solid are R x 6x and r x 0 respectively V Z 10 So the volume of the solid of revolution about the x axis is 6x 0 dx To find the volume integrate from x dx 243 to x horizontal axis of revolution