10th Class Mathematics Circles Question Bank Circle

  • question_answer
    In figure PQ is a chord of the circle and POR is its diameter such that \[\angle PRQ=50{}^\circ \]. If PT is the tangent to the circle at the point P then \[\angle QPT\]is equal to 

    A)  \[45{}^\circ \]                         

    B)  \[60{}^\circ \]

    C)  \[50{}^\circ \] 

    D)  \[55{}^\circ \]

    Correct Answer: C

    Solution :

    (c): In a figure, AOC is a diameter of the circle. Using the property that, diameter subtends an angle \[90{}^\circ \] to the circle. i.e., \[\angle PQR=90{}^\circ \] In \[\Delta \,PQR\], \[\angle P+\angle Q+\angle R=180{}^\circ ;\] \[\Rightarrow \]\[\text{ }\angle P+90{}^\circ +50{}^\circ =180{}^\circ \] \[\text{ }\angle P+180{}^\circ -140{}^\circ =40{}^\circ \] \[\because \] OP is perpendicular to PT;    \[\therefore \]\[\angle OPT=90{}^\circ \] \[\Rightarrow \]\[\angle OPQ+\angle QPT=90{}^\circ ;\] \[\Rightarrow \]\[\angle QPT=90{}^\circ -40{}^\circ =50{}^\circ \]                     


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