JEE Main & Advanced Mathematics Inverse Trigonometric Functions Question Bank Inverse trigonometric functions

  • question_answer
    \[2{{\tan }^{-1}}\left( \frac{1}{3} \right)+{{\tan }^{-1}}\left( \frac{1}{7} \right)=\]    [EAMCET 1983]

    A) \[{{\tan }^{-1}}\left( \frac{49}{29} \right)\]

    B) \[\frac{\pi }{2}\]

    C) 0

    D) \[\frac{\pi }{4}\]

    Correct Answer: D

    Solution :

    \[2{{\tan }^{-1}}\left( \frac{1}{3} \right)+{{\tan }^{-1}}\left( \frac{1}{7} \right)={{\tan }^{-1}}\left( \frac{2(1/3)}{1-(1/9)} \right)+{{\tan }^{-1}}\left( \frac{1}{7} \right)\] \[={{\tan }^{-1}}\frac{3}{4}+{{\tan }^{-1}}\frac{1}{7}={{\tan }^{-1}}\left( \frac{(3/4)+(1/7)}{1-(3/4)\times (1/7)} \right)\] \[={{\tan }^{-1}}\left( \frac{25}{25} \right)=\frac{\pi }{4}\].


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