qqp question1: S and T are the centers of their respective circles. The two circles are mutually tangent at point U. If segment RS = d, what is the radius of the smaller circle in terms of d and 'theta' (angle)? question2: When Given two circles with centers O and P, tangent to each other at A and a line tangent to both circles at B and C. Prove angle BAC is 90 degrees?