JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    If \[f(x)\,=\left| \,\begin{matrix}    \sin x & \cos x & \tan x  \\    {{x}^{3}} & {{x}^{2}} & x  \\    2x & 1 & 1  \\ \end{matrix}\, \right|\], then \[\underset{x\to 0}{\mathop{\lim }}\,\frac{f(x)}{{{x}^{2}}}\] is [Karnataka CET 2002]

    A)                 3

    B)                 ?1

    C)                 0

    D)                 1

    Correct Answer: D

    Solution :

                       \[f(x)=x(x-1)\sin x-({{x}^{3}}-2{{x}^{2}})\cos x-{{x}^{3}}\tan x\]                  \[={{x}^{2}}\sin x-{{x}^{3}}\cos x-{{x}^{3}}\tan x+2{{x}^{2}}\cos x-x\sin x\]            Hence \[\underset{x\to 0}{\mathop{\lim }}\,\frac{f(x)}{{{x}^{2}}}=\underset{x\to 0}{\mathop{\lim }}\,\,\left( \sin x-x\cos x-x\tan x+2\cos x-\left. \frac{\sin x}{x} \right) \right.\]                                                           \[=0-0-0+2-1=1\].


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