Manipal Engineering Manipal Engineering Solved Paper-2010

  • question_answer
    The point in the interval\[[0,\,\,2\pi ]\], where\[f(x)={{e}^{x}}\sin x\]has maximum slope, is

    A) \[\frac{\pi }{4}\]                                              

    B) \[\frac{\pi }{2}\]

    C) \[\pi \]                 

    D)        \[\frac{3\pi }{2}\]

    Correct Answer: B

    Solution :

    We have,\[f(x)={{e}^{x}}\sin x\] \[\Rightarrow \]               \[f(x)={{e}^{x}}\cos x+\sin x\cdot {{e}^{x}}\] and   \[f(x)=-\sin x\cdot {{e}^{x}}+\cos x\cdot {{e}^{x}}+\cos x\cdot {{e}^{x}}\]                                                                 \[+\sin x\cdot {{e}^{x}}\] Now, for maximum or minimum slope put                 \[(f(x))=0\Rightarrow f(x)=0\] \[\Rightarrow \]               \[2\cos x\cdot {{e}^{x}}=0\] \[\Rightarrow \]               \[\cos x=0\Rightarrow x=\frac{\pi }{2}\] Also, \[f(x)=-2\sin x\cdot {{e}^{x}}+2\cos x\cdot {{e}^{x}}=\]negative \[\therefore \]Slope is maximum at\[x=\pi /2\].


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