JEE Main & Advanced Mathematics Functions Question Bank Continuity

  • question_answer
    If the function \[f(x)=\left\{ \begin{align}   & 1+\sin \frac{\pi x}{2}\,\,,\,\text{for}\,-\infty <x\le 1 \\  & \,\,\,\,\,\,\,\,ax+b,\,\text{for}\,1<x<3 \\  & \,\,\,\,6\tan \frac{x\pi }{12},\,\text{for}3\le x<6 \\ \end{align} \right.\] is continuous in the interval \[(-\infty ,\,6)\], then the values of a and b are respectively [MP PET 1998]

    A)            0, 2

    B)            1, 1

    C)            2, 0

    D)            2, 1

    Correct Answer: C

    Solution :

               Given function is continuous at all point in \[(-\,\infty ,\,\,6)\] and at \[x=1,\,\,x=3\] function is continuous.                    If function \[f(x)\] is continuous at \[x=1,\] then                    \[\underset{x\to {{1}^{-}}}{\mathop{\lim }}\,\,f(x)=\underset{x\to {{1}^{+}}}{\mathop{\lim }}\,\,f(x)\]\[\Rightarrow \,\,\,1+\sin \frac{\pi }{2}=a+b\]                    \[\therefore \,\,\,a+b=2\]                                                        .....(i)                    If at \[x=3,\] function is continuous, then                    \[\underset{x\to {{3}^{-}}}{\mathop{\lim }}\,\,f(3)=\underset{x\to {{3}^{+}}}{\mathop{\lim }}\,\,f(x)\] \[\Rightarrow \,\,3a+b=6\tan \frac{3\pi }{12}\]                    \[\therefore \,\,\,3a+b=6\]                                                      .....(ii)            From (i) and (ii), \[a=2,\,\,b=0\] .


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