10th Class Mathematics Introduction to Trigonometry Question Bank Trigonometry

  • question_answer
    The angles of a quadrilateral are in A.P. and the greatest is double the least. Find the least angle in radian.

    A)  \[\frac{\pi }{6}\]                             

    B)         \[\frac{\pi }{4}\]

    C)  \[\frac{\pi }{3}\]                               

    D)         \[\frac{\pi }{5}\]

    Correct Answer: C

    Solution :

     Let the four angles of a quadrilateral are \[{{(a-3d)}^{o}},{{(a-d)}^{o}},{{(a+d)}^{o}}\] and \[{{(a+3d)}^{o}}\] \[\therefore \]  \[a-3d+a-d+a+d+a+3d={{360}^{o}}\] \[\therefore \]  \[a={{90}^{o}}\] But the greatest angle is double the least, i.e.                 \[a+3d=2\times (a-3d)\]                 \[=2a-6d\] \[\therefore \]  \[9a=2a-a\]                 \[=a\]                 \[={{90}^{o}}\] \[\therefore \]  \[d=\frac{90}{9}={{10}^{o}}\] \[\therefore \]  Least angle  \[=a-3d\]                 \[={{90}^{o}}-3\times {{10}^{o}}\]                 \[={{60}^{o}}\]                 \[=\frac{\pi }{3}\]


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