J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer
    If \[{{\tan }^{-1}}\,2\] and \[{{\tan }^{-1}}\,3\] are two angles of a triangle, then the third angle is

    A)  \[\frac{\pi }{2}\]

    B)  \[\frac{\pi }{3}\]

    C)  \[\frac{\pi }{4}\]

    D)  \[\frac{\pi }{6}\]

    Correct Answer: C

    Solution :

    Given two angles are \[{{\tan }^{-1}}2\] and \[{{\tan }^{-1}}3.\] Let third angle be \[\theta ,\] then, \[{{\tan }^{-1}}2+{{\tan }^{-1}}3+\theta ={{180}^{o}}\] \[\Rightarrow \] \[{{\tan }^{-1}}\left( \frac{2+3}{1-2\times 3} \right)={{180}^{o}}-\theta \] \[\Rightarrow \] \[\frac{5}{-5}=\tan ({{180}^{o}}-\theta )=-\tan \theta \] \[\Rightarrow \] \[\tan \theta =1=\tan \frac{\pi }{4}\] \[\Rightarrow \] \[\theta =\frac{\pi }{4}\]


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