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Math Help - Directional Derivatives

  1. #1
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    Directional Derivatives

    Can someone check my work. Im sure its wrong but i dont know where. Thanks
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  2. #2
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    Re: Directional Derivatives

    Did you treat (\frac{\pi}{2})^2+(9\pi)^2 as \frac{\pi^2}{2}+9\pi^2

    edit. making the above mistake and also having your calculator set to degrees gets a similar answer to what you got. It's hard to tell how you get from the 3rd last line to the 2nd last line.
    Last edited by Shakarri; October 9th 2013 at 11:24 AM.
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  3. #3
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    Re: Directional Derivatives

    Ive done the steps again, a little clearer this time. In Radian mode i get 0.

    Directional Derivatives-photo2.jpg
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  4. #4
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    Re: Directional Derivatives

    Yes, sine of any multiple of \pi is 0 (you shouldn't need a calculator for that). So grad f is the 0 vector. The directional derivative in any direction is 0
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  5. #5
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    Re: Directional Derivatives

    Thank you. It just didnt look correct. I didnt think all that work would lead to 0. Thanks for looking at this.
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