J & K CET Engineering J and K - CET Engineering Solved Paper-2003

  • question_answer
    If for some real number k \[\underset{x\to 0}{\mathop{\lim }}\,kx\,\,\text{cosec (x) =}\underset{x\to 0}{\mathop{\text{lim}}}\,\,\,x\,\,\text{cosec}\,\,(kx),\] then the possible values of k are

    A)  \[1,-1\]                                                

    B)  \[0,\,\,\,1\]

    C)  \[1,\,\,\,2\]

    D)  \[0,\,\,\,\pi \]

    Correct Answer: A

    Solution :

    Given that, \[\underset{x\to 0}{\mathop{\lim }}\,\,\,kx\,\text{cosec (x)=}\underset{x\to 0}{\mathop{\text{lim}}}\,x\,\text{cosec (kx)}\] \[\Rightarrow \] \[k\,\underset{x\to 0}{\mathop{\lim }}\,\,\frac{x}{\sin \,\,x}=\,\underset{x\to 0}{\mathop{\lim }}\,\,\frac{x}{\sin \,kx}\times \frac{k}{k}\] \[\Rightarrow \] \[k=\frac{1}{k}\] \[\Rightarrow \] \[{{k}^{2}}=1\] \[\Rightarrow \] \[k=\pm 1\]


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