J & K CET Engineering J and K - CET Engineering Solved Paper-2007

  • question_answer
    \[\underset{x\to 0}{\mathop{\lim }}\,\frac{1}{x}{{\sin }^{-1}}\left( \frac{2x}{1+{{x}^{2}}} \right)\]is equal to

    A)  \[-2\]            

    B)  \[0\]

    C)  \[2\]               

    D)  \[\infty \]

    Correct Answer: C

    Solution :

    Put \[x=\tan \theta \Rightarrow \theta ={{\tan }^{-1}}x\] \[\therefore \] \[\underset{x\to 0}{\mathop{\lim }}\,\frac{1}{x}{{\sin }^{-1}}\left( \frac{2\,\tan \theta }{1+{{\tan }^{2}}\theta } \right)\] \[=\underset{x\to 0}{\mathop{\lim }}\,\frac{1}{x}\,{{\sin }^{-1}}(\sin 2\theta )\] \[=\underset{x\to 0}{\mathop{\lim }}\,\frac{1}{x}\,.2\theta =\underset{x\to 0}{\mathop{\lim }}\,\frac{2{{\tan }^{-1}}x}{x}\] \[=2\times \underset{x\to 0}{\mathop{\lim }}\,\,\frac{{{\tan }^{-1}}x}{x}\] \[=2\times 1=2\]


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