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

  • question_answer
    If\[f(x)=\left\{ \begin{matrix}    mx+1x\le \frac{\pi }{2}  \\    \sin x+nx>\frac{\pi }{2}  \\ \end{matrix}\,\,\,\text{is}\,\,\text{continuous}\,\,\text{at} \right.\]\[x=\frac{\pi }{2}\], then which one of the following is correct?

    A) m = 1, n = 0

    B) \[m=\frac{n\pi }{2}+1\]

    C) \[n=m\left( \frac{\pi }{2} \right)\]

    D) \[m=n=\frac{\pi }{2}\]

    Correct Answer: C

    Solution :

    [c] Given function is
    \[f(x)=\left\{ \begin{matrix}    mx+1, & x\le \frac{\pi }{2}  \\    \sin x+n, & x>\frac{\pi }{2}  \\ \end{matrix} \right.\]
    As given this function is continuous at \[x=\frac{\pi }{2}\].
    So, limit of function when \[x\to \frac{\pi }{2}=f\left( \frac{\pi }{2} \right)\]
    \[\Rightarrow \underset{x\to \frac{\pi }{2}+}{\mathop{\lim }}\,(\sin \,x+n)=f\left( \frac{\pi }{2} \right)\]
    \[\Rightarrow \underset{h\to 0}{\mathop{\lim }}\,\left( \sin \left( \frac{\pi }{2}+h \right)+n \right)=\frac{m\pi }{2}+1\]
    \[\Rightarrow \sin \frac{\pi }{2}+n=\frac{m\pi }{2}+1\]
    \[\Rightarrow 1+n=\frac{m\pi }{2}+1\]
    \[\Rightarrow n=\frac{m\pi }{2}\]


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