In Figure, AB and CD are common tangents to two circles of unequal radii. Prove that AB = CD.
                
                  To Prove: AB = CD
Extend AB and CD then they meet at point E.
Here EA = EC     (  length of tangent drawn from the same point is equal)
Also EB = ED       (  length of tangent drawn from some point is equal)
AB = AE - BE
CD = CE -DF
From equal axiom if equal are subtracted from equal then the result is equal.
Hence Proved