# distance between centers of two touching circles

Lets say we have two circles with radii 2 and 3 respectively.

If we then put Circle radius 2 on a flat surface, then the other circle on the flat surface so they touch once, what is the distance between the two centers?

A the point of contact the circles share a mutual external tangent and so the two radii are both perpendicular to that line. Therefore the center to center distance is simply $r_1 + r_2$, in this case $2 + 3 = 5$.