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Math Help - Stationary point...

  1. #1
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    Stationary point...

    Find the coordinates of the stationary point of the curve y=e^xcosx for 0 is less than or equal to x and x is less than or equal to /pi . Leave your answer in exact form.
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    Quote Originally Posted by Punch View Post
    Find the coordinates of the stationary point of the curve y=e^xcosx for 0 is less than or equal to x and x is less than or equal to x . Leave your answer in exact form.
    First get dy/dx (use the product rule). Can you do that? Please show all your work and say where you're stuck.
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    <br />
dy/dx=-e^xsinx<br />

    am stucked at the part solving for x
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    Quote Originally Posted by Punch View Post
    <br />
dy/dx=-e^xsinx<br />
    [snip]
    Wrong. Have you been taught the product rule? If not, then attempting this question is currently a futile exercise for you. If you have, then I suggest you go to your class notes or textbook and review it.
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  5. #5
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    \frac{dy}{dx} = e^xcosx-e^xsinx
    = e^x[cosx-sinx]




    now, e^x[cosx-sinx]=0 stucked =="
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  6. #6
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    Quote Originally Posted by Punch View Post
    \frac{dy}{dx} = e^xcosx-e^xsinx
    = e^x[cosx-sinx]
    Correct.

    Now solve \frac{dy}{dx} = 0 \Rightarrow \cos x - \sin x = 0 \Rightarrow 1 = \tan x over the given domain.

    Then find the y-coordinate corresponding to the solutions for x found above.

    If you need more help, please show all your work and say where you get stuck.
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  7. #7
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    i dont understand the part where u "threw" e^x away... wont u lose a solution? other than this everything else is fine thx
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  8. #8
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    Quote Originally Posted by Punch View Post
    i dont understand the part where u "threw" e^x away... wont u lose a solution? other than this everything else is fine thx
    Do you know what the graph of y = e^x looks like? Can e^x ever equal zero?
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