Question

Two spheres with the same radius , one centered at (1,2,-4) and the other centered at (2,4,3), touch each other tangentially at a single point. Find the value of the radius

Answer 1

http://www.wolframalpha.com/input/?i=%28x-1%29^2%2B%28y-2%29^2%2B%28z%2B4%29^2%3Dr^2%2C%28x-2%29^2%2B%28y-4%29^2%2B%28z-3%29^2%3Dr^2

Radius: \[3\sqrt{\frac{3}{2}}\]