JEE Main & Advanced Mathematics Functions Question Bank Differentiability

  • question_answer
    The function defined by \[f(x)=\left\{ \begin{align}   & |x-3|\,;\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\ge 1 \\  & \frac{1}{4}{{x}^{2}}-\frac{3}{2}x+\frac{13}{4};\,x<1 \\ \end{align} \right.\] is [IIT 1988]

    A)                    Continuous at \[x=1\]

    B)            Continuous at \[x=3\]

    C)            Differentiable at \[x=1\]

    D)            All the above

    Correct Answer: D

    Solution :

               Since  \[|x-3|\,=x-3,\] if \[x\ge 3\]\[=-x+3,\] if \[x<3\]                    \[\therefore \] The given function can be defined as                    \[f(x)=\left\{ \begin{array}{*{35}{r}}    \frac{1}{4}{{x}^{2}}-\frac{3}{2}x+\frac{13}{4}, & x<1\,\,\,\,\,\,\,\,  \\    3-x, & 1\le x<3  \\    x-3, & x\ge 3\,\,\,\,\,\,\,  \\ \end{array} \right.\]            Now proceed to check the continuity and differentiability at \[x=1.\]


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