10th Class Mathematics Circles Question Bank Circles

  • question_answer
    In the given figure, PT touches the circle at R whose centre is O. Diameter SQ when produced meets PT at P. Given \[\angle SPR={{x}^{o}}\]and \[\angle QRP={{y}^{o}}\]. Then,

    A) \[{{x}^{o}}+2{{y}^{o}}={{90}^{o}}\]         

    B) \[2{{x}^{o}}+{{y}^{o}}={{90}^{o}}\]

    C)          \[{{x}^{o}}+{{y}^{o}}={{120}^{o}}\]

    D)        \[3{{x}^{o}}+2{{y}^{o}}={{120}^{o}}\]

    Correct Answer: A

    Solution :

    Consider chord QR \[\therefore \]   \[\angle QRP=\angle QSR\] \[\Rightarrow \]            \[\angle QSR={{y}^{o}}\]               \[[\because \,\,\,\angle QRP={{y}^{o}}]\] \[\Rightarrow \]            \[\angle PSR={{y}^{o}}\] Since angle in a semicircle is a right angle. \[\therefore \]  \[\angle QRS={{90}^{o}}\] Now, \[\angle PRS=\angle QRP+\angle QRS\Rightarrow \angle PRS={{y}^{o}}+{{90}^{o}}\]In \[\Delta \,PRS,\] we have \[\angle SPR+\angle PRS+\angle PSR={{180}^{o}}\] \[\Rightarrow \] \[{{x}^{o}}+{{y}^{o}}+{{90}^{o}}+{{y}^{o}}={{180}^{o}}\] [Given,\[\angle SPP={{x}^{o}}\]]             \[\Rightarrow \]            \[{{x}^{o}}+2{{y}^{o}}={{90}^{o}}\]


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