MathDB
Externally Tangent Circles

Source:

November 13, 2005
quadraticsgeometrytrapezoidnumber theoryrelatively primePythagorean Theoremalgebra

Problem Statement

Circles C1C_1 and C2C_2 are externally tangent, and they are both internally tangent to circle C3C_3. The radii of C1C_1 and C2C_2 are 44 and 1010, respectively, and the centers of the three circles are all collinear. A chord of C3C_3 is also a common external tangent of C1C_1 and C2C_2. Given that the length of the chord is mnp\frac{m\sqrt{n}}{p} where m,n,m,n, and pp are positive integers, mm and pp are relatively prime, and nn is not divisible by the square of any prime, find m+n+pm+n+p.