1.

A quadrilateral ABCD is drawn to circumscribe a circle (see the fig. given below). Prove that AB + CD = AD + BC.

Answer»

Data: In the quadrilateral, ABCD is drawn to circumscribe a circle. 

To Prove: AB + CD = AD + BC 

The lengths of tangents drawn from an extrenal point to a circle are equal. 

∴ Tangents AP and AS are drawn from point A. 

∴ AP = AS Tangents BP and BQ are drawn from point B. 

∴ BP = BQ Tangents CQ, CR are drawn from point C. 

∴ CQ = CR. Tangents DR, DS are drawn from point A. 

∴ DR = DS 

L.H.S.: AB + CD = AP + PB + CR + RD 

= AS + BQ + CQ + DS 

= AS + SD + BQ + CQ 

∴ AB + CD = AD + BC 

∴ L.H.S. = R.H.S.



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