JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    \[\underset{h\to 0}{\mathop{\lim }}\,\frac{2\left[ \sqrt{3}\sin \left( \frac{\pi }{6}+h \right)-\cos \left( \frac{\pi }{6}+h \right) \right]}{\sqrt{3}h(\sqrt{3}\cos h-\sin h)}=\] [BIT Ranchi 1987]

    A)                 \[-\frac{2}{3}\]

    B)                 \[-\frac{3}{4}\]

    C)                 \[-2\sqrt{3}\]

    D)                 \[\frac{4}{3}\]

    Correct Answer: D

    Solution :

                       \[\underset{h\to 0}{\mathop{\lim }}\,\,\frac{2\,\left[ \sqrt{3}\sin \,\left( \frac{\pi }{6}+h \right)-\cos \,\left( \frac{\pi }{6}+h \right) \right]}{\sqrt{3}\,h\,(\sqrt{3}\,\cos \,h-\sin \,h)}\]                    \[=\underset{h\to 0}{\mathop{\lim }}\,\,\frac{\frac{4}{\sqrt{3}}\,\left[ \frac{\sqrt{3}}{2}\sin \,\left( \frac{\pi }{6}+h \right)-\frac{1}{2}\cos \,\left( \frac{\pi }{6}+h \right) \right]}{h\,(\sqrt{3}\cos \,h-\sin \,h)}\]                                 \[=\underset{h\to 0}{\mathop{\lim }}\,\frac{4}{\sqrt{3}}.\frac{\sin \,h}{h}.\frac{1}{(\sqrt{3}\,\cos \,h-\sin \,h)}=\frac{4}{3}\].


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