Geometry Problem 485: Square, Side, Circles, Tangent, Radius, Measurement

The figure shows a square ABCD of side
a. Circles C_{1}, C_{2}, C_{3}, C_{4},
are tangent to each other and to the sides of the square.
Circles C_{1} and C_{2}, are congruent. Circles
C_{3} and C_{4},are congruent with radii x.
Prove that
.