JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{x\to 1}{\mathop{\lim }}\,\frac{1+\cos \pi \,x}{{{\tan }^{2}}\pi \,x}\] is equal to [AMU 2001]

    A)                 0

    B)                 1/2

    C)                 1

    D)                 2

    Correct Answer: B

    Solution :

                       \[\underset{x\to 1}{\mathop{\lim }}\,\frac{(1+\cos \pi x)}{{{\tan }^{2}}\pi x}=\underset{x\to 1}{\mathop{\lim }}\,\frac{-\pi \sin \pi x}{2\pi \tan \pi x{{\sec }^{2}}\pi x}\]                                                                               [Using L-Hospital?s rule] \[=\underset{x\to 1}{\mathop{\lim }}\,\frac{-1}{2}{{\cos }^{3}}\pi \,x\]\[=\frac{1}{2}\].


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