In the given figure, a circle is inscribed in quad. ABCD. If BC=38cm,BQ=27cm,DC=25cm and AD⊥DC. The radius of the circle is
A
28cm
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B
21cm
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C
14cm
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D
42cm
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Solution
The correct option is C 14cm Given−Oisthecentreofacircle,inscribedinaquadrilateralABCD.Theradiusofthecircleis10cm.DC,BC,AB&ADtouchtheinscribedcircleatP,Q,R&Srespectively.BQ=27cm,BC=38cm&DC=25cm.AD⊥DC.Tofindout−Theradiusofthecircle=?Solution−WejoinOS&OP.ThenOS&OPareradiioftheinscribedcirclethroughthepointsofcontactofthetangentsAS&APrespectively.∴OS=OP.Also∠ADC=90osinceAD⊥DC.NowinOSDP,∠PAS=90oandOS=OP,DP=DSsincethelengthsofthetangents,fromapointtoacircle,areequa.∴OSDPisasquareofside.SoDP=OS.AgainBQ=BR=27cmandCQ=CPsincethelengthsofthetangents,fromapointtoacircle,areequal.∴CQ=BC−BQ=(38−27)cm=11cm.AlsoCP=CQ=11cm.∴DP=OS=DC−CP=(25−11)cm=14cm.Sotheradiusofthecircleis14cm.Ans−OptionC.