A quadrilateral ABCD is drawn to circumscribe a circle. Prove that AB + CD = AD + BC.
To prove: AB + CD = AD + BC.
Proof: AS = AP ( Length of tangents from an external point to a circle are equal)
BQ = BP
CQ = CR
DS = DR
AS + BQ + CQ + DS = AP + BP + CR + DR
(AS + DS) + ( BQ + CQ) = (AP + BP) + (CR + DR)
AD + BC = AB +CD