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

  • question_answer
    If \[\theta \] are the points of discontinuity of \[f(x)=\underset{n\to \infty }{\mathop{\lim }}\,{{\cos }^{2n}}x\] then the value of sin \[\theta \] is

    A) 0

    B) 1

    C) -1

    D) ½

    Correct Answer: A

    Solution :

    [a] \[f(x)=\underset{n\to \infty }{\mathop{\lim }}\,{{({{\cos }^{2}}x)}^{n}}\] \[=\left\{ \begin{matrix}    0, & 0\le {{\cos }^{2}}x<1  \\    1, & {{\cos }^{2}}x=1  \\ \end{matrix}=\left\{ \begin{matrix}    0, & x\ne n\pi ,n\in I  \\    1, & x=n\pi ,n\in I  \\ \end{matrix} \right. \right.\] Hence, \[f(x)\] is discontinuous when \[x=n\pi ,n\in I\] For this values of \[\theta ,\sin \theta =0\].


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