The figure shows a line ABCD = d with
circles C1 of diameter AB and circle C2 of
diameter CD. AE and AF are tangent to circle C2, DG
and DH are tangent to circle C1. Circle C3
of radius r3 is tangent to C1, AE and AF
at B, K and L, respectively. Circle C4 of radius r4
is tangent to C2, DG and DH at C, N and P,
respectively. Prove that
.
See also: Problem
525.
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