BCECE Engineering BCECE Engineering Solved Paper-2007

  • question_answer
    The value of \[\underset{\alpha \to 0}{\mathop{\lim }}\,\frac{\begin{align}   & \cos e{{c}^{-1}}(sec\alpha )+co{{t}^{-1}}(tan\alpha ) \\  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,+co{{t}^{-1}}\cos (si{{n}^{-1}}\alpha ) \\ \end{align}}{\alpha }\]is

    A)  0                            

    B)         \[-1\]                   

    C)  \[-2\]                   

    D)         1

    Correct Answer: C

    Solution :

    \[\underset{\alpha \to 0}{\mathop{\lim }}\,\frac{\begin{align}   & \cos e{{c}^{-1}}(sec\alpha )+co{{t}^{-1}}(tan\alpha ) \\  & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,+co{{t}^{-1}}\cos (si{{n}^{-1}}\alpha ) \\ \end{align}}{\alpha }\] \[=\underset{\alpha \to 0}{\mathop{\lim }}\,\frac{\left[ \begin{align}   & \cos e{{c}^{-1}}\left( \cos ec\left( \frac{\pi }{2}-\alpha  \right) \right) \\  & +{{\cot }^{-1}}\left( \cot \left( \frac{\pi }{2}-\alpha  \right) \right) \\  & +\,{{\cot }^{-1}}\cos [co{{s}^{-1}}\sqrt{1-{{\alpha }^{2}}}] \\ \end{align} \right]}{\alpha }\] \[=\underset{\alpha \to 0}{\mathop{\lim }}\,\frac{\frac{\pi }{2}-\alpha +\frac{\pi }{2}-\alpha +{{\cot }^{-1}}\sqrt{1-{{\alpha }^{2}}}}{\alpha }\] \[=\underset{\alpha \to 0}{\mathop{\lim }}\,\frac{-2-\frac{1}{1+1-{{\alpha }^{2}}}\left( \frac{1}{2\sqrt{1-{{\alpha }^{2}}}}(-2\alpha ) \right)}{1}\] \[=-2\]


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