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

  • question_answer
    Consider the function \[f(x)=\left\{ \begin{matrix}    ax-2 & for & -2<x<-1  \\    -1 & for & -1\le x\le 1  \\    a+2{{(x-1)}^{2}} & for & 1<x<2  \\ \end{matrix} \right.\] What is the value of a for which f(x) is continuous at x =-1 and x=1?

    A) -1

    B) 1

    C) 0

    D) 2

    Correct Answer: A

    Solution :

    [a] \[f(x)=\left\{ \begin{matrix}    ax-2 & -2<x<-1  \\    -1 & -1\le x\le 1  \\    a+2{{(x-1)}^{2}} & 1<x<2  \\ \end{matrix} \right.\] If f(x) is continuous at x = -1 then, \[\underset{x\to -1}{\mathop{\lim }}\,(ax-2)=\underset{x\to -1}{\mathop{\lim }}\,(-1)\] \[\Rightarrow a(-1)-2=-1\Rightarrow a=-1\] If f(x) is continuous at x = 1 then, \[\underset{x\to 1}{\mathop{\lim }}\,a+2{{(x-1)}^{2}}=\underset{x\to 1}{\mathop{\lim }}\,-1\] \[\Rightarrow a+2{{(1-1)}^{2}}=-1\Rightarrow a=-1\]


You need to login to perform this action.
You will be redirected in 3 sec spinner