JEE Main & Advanced Mathematics Limits, Continuity and Differentiability Question Bank Self Evaluation Test - Continuity and Differentiability

  • question_answer
    What is \[\underset{x\to 0}{\mathop{\lim }}\,\frac{2(1-\cos x)}{{{x}^{2}}}\] equal to?

    A) 0

    B) 1/2

    C)  ¼

    D) 1

    Correct Answer: D

    Solution :

    [d] \[\underset{x\to 0}{\mathop{\lim }}\,\frac{2(1-\cos \,x)}{{{x}^{2}}}=\underset{x\to 0}{\mathop{\lim }}\,\frac{2.2\,\,{{\sin }^{2}}\frac{x}{2}}{{{x}^{2}}}\] \[=4\,\underset{x\to 0}{\mathop{\lim }}\,\frac{\sin \frac{x}{2}}{\frac{x}{2}\times 2}.\underset{x\to 0}{\mathop{\lim }}\,\frac{\sin \frac{x}{2}}{\frac{x}{2}\times 2}\] \[=\underset{x\to 0}{\mathop{\lim }}\,\frac{\sin \frac{x}{2}}{\frac{x}{2}}.\underset{x\to 0}{\mathop{\lim }}\,\frac{\sin \frac{x}{2}}{\frac{x}{2}}=1\times 1=1\]


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