In fig. 2, a circle with centre O is inscribed in a quadrilateral ABCD such that, it touchesthe sides BC, AB, AD and CD at points P, Q, R and S respectively. If AB=29cm, AD=23,B= 90 and DS=5cm, then the radius of the circle (in cm.) is:


Given,AB=29cm,AD=23cm, B=900,DS=5cm Join OP and OQ.Then,OP=OQ, OPPB OQBQ OPBQ is a square. Tangles from an external point,being equal,we have: DS=DR, BP=QB, AS=APDS=DR=5cmAS=18cm [235] also AP=18cm PB=ABAP =2918 =11cm OQ=11cm The radius is 11cm.

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