JEE Main & Advanced JEE Main Paper (Held on 08-4-2019 Morning)

  • question_answer
    If\[\alpha ={{\cos }^{-1}}\left( \frac{3}{5} \right),\beta ={{\tan }^{-1}}\left( \frac{1}{3} \right),\]where\[0<\alpha ,\beta <\frac{\pi }{2},\]then\[\alpha -\beta \]is equal to: [JEE Main 8-4-2019 Morning]

    A) \[{{\sin }^{-1}}\left( \frac{9}{5\sqrt{10}} \right)\]

    B) \[{{\tan }^{-1}}\left( \frac{9}{14} \right)\]

    C) \[{{\cos }^{-1}}\left( \frac{9}{5\sqrt{10}} \right)\] 

    D) \[{{\tan }^{-1}}\left( \frac{9}{5\sqrt{10}} \right)\]

    Correct Answer: A

    Solution :

                \[\cos \alpha =\frac{3}{5},\tan \beta =\frac{1}{3}\]\[\Rightarrow \]\[\tan \alpha =\frac{4}{3}\]           \[\Rightarrow \]\[\tan (\alpha -\beta )=\frac{\frac{4}{3}-\frac{1}{3}}{1+\frac{4}{3}.\frac{1}{3}}=\frac{9}{13}\]           \[\Rightarrow \]\[sin(\alpha -\beta )=\frac{9}{5\sqrt{10}}\]\[\Rightarrow \]\[\alpha -\beta ={{\sin }^{-1}}\left( \frac{9}{5\sqrt{10}} \right)\]


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