Question

A region is bounded by y = 3x, x-axis and x=5. What is the volume of this region revolved about the y axis?

Answer 1

this is a cylinder minus a cone, or you can do some calculus (volume of revolution) but why would you bother...

Answer 2

but whatever you're doing, first draw it out. that usually really helps.

Answer 3

oh, yes, drawing it out does help a lot. Thanks for the pointer!