JEE Main & Advanced Mathematics Functions Question Bank Continuity

  • question_answer
    In the function \[f(x)=\frac{2x-{{\sin }^{-1}}x}{2x+{{\tan }^{-1}}x},\ (x\ne 0)\]is continuous at each point of its domain, then the value of \[f(0)\] is [RPET 2000]

    A)            2

    B)            \[1/3\]

    C)            \[2/3\]

    D)            \[-1/3\]

    Correct Answer: B

    Solution :

               \[f(x)=\underset{x\to 0}{\mathop{\lim }}\,\,\left( \frac{2x-{{\sin }^{-1}}x}{2x+{{\tan }^{-1}}x} \right)=f(0)\],           \[\left( \frac{0}{0} \right)\]            Applying L-Hospital?s rule,            \[f(0)=\underset{x\to 0}{\mathop{\lim }}\,\frac{\left( 2-\frac{1}{\sqrt{1-{{x}^{2}}}} \right)}{\left( 2+\frac{1}{1+{{x}^{2}}} \right)}\] \[=\frac{2-1}{2+1}=\frac{1}{3}\]                    Trick : f (0) =\[\underset{x\to 0}{\mathop{\lim }}\,\frac{2-\frac{{{\sin }^{-1}}x}{x}}{2+\frac{{{\tan }^{-1}}x}{x}}=\frac{2-1}{2+1}=\frac{1}{3}\].


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