If you have the net of cone (excluding a circular base).

So it is a sector of a circle, with the radius given.

Can you work out the would be height of the circle by doing -

exterior sector angle / 360 = x

x times diameter of circle = answer

Just wondering if someone could proof it.. using perhaps a different cyclinder to the one below?

http://www.yummiehost.com/images/44144cone.png

(dont need question answering, but thats where the idea comes from)

Thanks,

Alex.