BCECE Engineering BCECE Engineering Solved Paper-2001

  • question_answer
    If \[{{\cos }^{-1}}\left( \frac{1}{x} \right)=\theta ,\] then tan 9is equal to:

    A) \[\frac{1}{\sqrt{{{x}^{2}}}-1}\]                  

    B)  \[\sqrt{{{x}^{2}}+1}\]   

    C)         \[\sqrt{1-{{x}^{2}}}\]

    D)                         \[\sqrt{{{x}^{2}}-1}\]

    Correct Answer: D

    Solution :

    If \[{{\cos }^{-1}}\left( \frac{1}{x} \right)=\theta \] \[\frac{1}{x}=\cos \theta \]                         Now,     \[\tan \theta =\frac{\sin \theta }{\cos \theta }\]                                 \[=\frac{\sqrt{1-{{\cos }^{2}}\theta }}{\cos \theta }=\frac{\sqrt{1-\frac{1}{{{x}^{2}}}}}{\frac{1}{x}}\] \[=\sqrt{{{x}^{2}}-1}\]


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