10th Class Mathematics Circles Question Bank Circles

  • question_answer
    In the given figure, O is the centre of a circle; PQL and PRM are the tangents at the points Q and R respectively and S is a point on the circle such that \[\angle SQL={{50}^{o}}\]and \[\angle SRM={{60}^{o}}\]. Then, find \[\angle QSR\] and \[\angle RPQ\].

    A) \[{{40}^{o}},{{140}^{o}}\]                    

    B)        \[{{50}^{o}},{{140}^{o}}\]                    

    C)                    \[{{60}^{o}},{{120}^{o}}\]                    

    D)        \[{{70}^{o}},\text{ }{{40}^{o}}\]    

    Correct Answer: D

    Solution :

    Since, PQL is a tangent and OQ is a radius, so\[\angle OQL={{90}^{o}}\] \[\therefore \]    \[\angle OQS=({{90}^{o}}-{{50}^{o}})={{40}^{o}}\]          Now, \[OQ=OS\Rightarrow \angle OSQ=\angle OQS={{40}^{O}}\] Similarly, \[\angle ORS=({{90}^{o}}-{{60}^{o}})={{30}^{o}}\] And, \[OR=OS\Rightarrow \angle OSR=\angle ORS={{30}^{o}}\] \[\therefore \]\[\angle QSR=\angle OSQ+\angle OSR=({{40}^{o}}+{{30}^{o}})={{70}^{o}}\] Now,  \[\angle ROQ=2\,\,\,\angle QSR={{140}^{o}}\] \[\angle ROQ+\,\,\angle ORP+\angle OQP+\angle RPQ={{360}^{o}}\] (Angle sum property of quadrilateral QORP) \[\Rightarrow \]            \[{{140}^{o}}+{{90}^{o}}+{{90}^{o}}+\angle RPQ={{360}^{o}}\] \[\Rightarrow \]            \[\angle RPQ={{40}^{o}}\]


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