1. ## tetrahedron

Find radius of the incircle of a regular tetrahedron the length of each side being $k$ units.

2. Originally Posted by pankaj
Find radius of the incircle of a regular tetrahedron the length of each side being $k$ units.
I assume that you mean the insphere. If so have a look here:
Tetrahedron - Wikipedia, the free encyclopedia

If a is the length of one edge then the radius of the insphere is $r = \dfrac a{\sqrt{24}}$