Manipal Engineering Manipal Engineering Solved Paper-2011

  • question_answer
    If\[f(x)=|x{{|}^{|\sin x|}}\], then\[f\left( -\frac{\pi }{4} \right)\]is equal to

    A) \[{{\left( \frac{\pi }{4} \right)}^{1/\sqrt{2}}}\left( \frac{\sqrt{2}}{2}\log \frac{4}{\pi }-\frac{2\sqrt{2}}{\pi } \right)\]

    B) \[{{\left( \frac{\pi }{4} \right)}^{1/\sqrt{2}}}\left( \frac{\sqrt{2}}{2}\log \frac{4}{\pi }+\frac{2\sqrt{2}}{\pi } \right)\]

    C) \[{{\left( \frac{\pi }{4} \right)}^{1/\sqrt{2}}}\left( \frac{\sqrt{2}}{2}\log \frac{\pi }{4}-\frac{2\sqrt{2}}{\pi } \right)\]

    D) \[\left( \frac{\sqrt{2}}{2}\log \frac{\pi }{4}+\frac{2\sqrt{2}}{\pi } \right)\]

    Correct Answer: A

    Solution :

    Since,    \[f(x)=|x{{|}^{\sin x}}\] when\[x<0\]                 \[f(x)={{(-x)}^{(-\sin x)}}\]                 \[={{e}^{-\sin x\log (-x)}}\] \[\Rightarrow \]               \[f(x)={{e}^{-\sin x\log (-x)}}\]                                 \[\left( -\cos x\log (-x)-\frac{\sin x}{x} \right)\] \[\Rightarrow \]               \[f(x)={{(-x)}^{-\sin x}}\]                                 \[\left( -\cos x\cdot \log (-x)-\frac{\sin x}{x} \right)\] \[\Rightarrow \]               \[f\left( -\frac{\pi }{4} \right)={{\left( \frac{\pi }{4} \right)}^{1/\sqrt{2}}}\]                                 \[\left( -\frac{1}{\sqrt{2}}\log \frac{\pi }{4}+\frac{4}{\pi }\left( -\frac{1}{\sqrt{2}} \right) \right)\]                 \[={{\left( \frac{\pi }{4} \right)}^{1/\sqrt{2}}}\left( \frac{\sqrt{2}}{2}\log \frac{4}{\pi }-\frac{2\sqrt{2}}{\pi } \right)\]


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