JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2005

  • question_answer
        \[\underset{x\to 0}{\mathop{\lim }}\,\frac{\sqrt{1-\cos 2x}}{\sqrt{2}x}\]is:

    A)  \[\lambda \]

    B)  \[-1\]

    C)  zero

    D)  does not exist

    Correct Answer: D

    Solution :

                    \[\underset{x\to 0}{\mathop{\lim }}\,\frac{\sqrt{1-\cos 2x}}{\sqrt{2}x},\] \[\Rightarrow \]               \[\underset{x\to 0}{\mathop{\lim }}\,\frac{\sqrt{1-(1-2{{\sin }^{2}}x)}}{\sqrt{2}x}\]                 \[\underset{x\to 0}{\mathop{\lim }}\,\frac{\sqrt{2{{\sin }^{2}}x}}{\sqrt{2}x}\Rightarrow \underset{x\to 0}{\mathop{\lim }}\,\frac{|\sin x|}{x}\] So,          \[f(x)=\frac{|\sin x|}{x}\] Now, \[f(0+0)=\underset{h\to 0}{\mathop{\lim }}\,\frac{|\sin (0+h)|}{0+h}\]                 \[=\underset{h\to 0}{\mathop{\lim }}\,\frac{\sin \,h}{h}=1\]                 \[f(0-0)=\underset{h\to 0}{\mathop{\lim }}\,\frac{|\sin (0-h)|}{-h}\]                 \[\underset{h\to 0}{\mathop{\lim }}\,\frac{\sin h}{-h}=-1\] \[\because \]     \[F(0+0)\ne f(0-0)\]the limit of function does not exist.


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