# Math Help - Volume of a right circular cone

1. ## Volume of a right circular cone

I wouldn't even know where to begin with this problem. Any suggestions?

2. Originally Posted by fattydq
I wouldn't even know where to begin with this problem. Any suggestions?
The volume of a right circular cone is $V=\frac13\pi r^2h\text.$ It looks like you almost had it, but the given radius is $5r,$ not $5\pi\text.$

If you want to derive the formula, an easy way to do it is to position a right triangle such that its right angle is at the origin and its two legs along the $x$- and $y$-axes, and find the volume of the solid resulting from revolving the triangular region about one of the axes.

3. Thanks, you've been replying in several of my threads, thank you very much. I've been drilling myself for a test this friday and I'm solid on everything but volumes.