2004 AIME II Problems/Problem 12
Problem
Let be an isosceles trapezoid, whose dimensions are and Draw circles of radius 3 centered at and and circles of radius 2 centered at and A circle contained within the trapezoid is tangent to all four of these circles. Its radius is where and are positive integers, is not divisible by the square of any prime, and and are relatively prime. Find
Solution
Let the radius of the center circle be and its center be denoted as . The center obviously has an x-coordinate of .
So line passes through the point of tangency of circle and circle . Now let be height from the base of trapezoid to O. Now, from Pythagoreum Theorem, .
We use a similar argument with the line , and find the height from the top of the trapezoid to , , to be .
Now , so we solve the equation
Solving this, we get
So .