Let *a*, *b*, and *c* be the sides of a triangle.

Let *p* be perimeter of the triangle.

Let *r* be the radius of the largest circle that can be inscribed in the triangle, and let *R* be the radius of the circle through the vertices of the triangle.

Then all six numbers can be related in one equation:

2*prR* = *abc.*

Dr Cook,

Thanks love the way we can use there together. But, am I missing something? The equation appears to be off by a factor of 2.

Should be 4prR = abc

Perhaps you’re thinking of the equation in the form 4srR = abc where s is the semiperimeter, s = p/2.