JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{x\to \pi /2}{\mathop{\lim }}\,\left[ x\tan x-\left( \frac{\pi }{2} \right)\sec x \right]=\]

    A)                 1

    B)                 ?1

    C)                 0

    D)                 None of these

    Correct Answer: B

    Solution :

                       \[\underset{x\to \pi /2}{\mathop{\lim }}\,\,\left[ x\tan x-\left( \frac{\pi }{2} \right)\,\sec x \right]\]            \[=\underset{x\to \pi /2}{\mathop{\lim }}\,\,\,\frac{2x\,\,\sin x-\pi }{2\,\cos x}\],                           \[\left[ \text{form}\frac{0}{0} \right]\]                                 \[=\underset{x\to \pi /2}{\mathop{\lim }}\,\,\,\frac{[2\,\sin x+2x\cos x]}{-2\,\sin x}=-1\],(By L-Hospital?s rule).


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