JEE Main & Advanced Mathematics Circle and System of Circles Question Bank Tangent and normal to a circle

  • question_answer
    The angle between the two tangents from the origin to the circle \[{{(x-7)}^{2}}+{{(y+1)}^{2}}=25\] is [MNR 1990; RPET 1997; DCE 2000]

    A)            0    

    B)            \[\frac{\pi }{3}\]

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

    D)            \[\frac{\pi }{2}\]

    Correct Answer: D

    Solution :

               Any line through (0, 0) be \[y-mx=0\] and it is a tangent to circle\[{{(x-7)}^{2}}+{{(y+1)}^{2}}=25\], if                    \[\frac{-1-7m}{\sqrt{1+{{m}^{2}}}}=5\Rightarrow m=\frac{3}{4},\ -\frac{4}{3}\].                    Therefore, the product of both the slopes is -1.                    i.e., \[\frac{3}{4}\times -\frac{4}{3}=-1\].                    Hence the angle between the two tangents is\[\frac{\pi }{2}\].


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