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Math Help - Find the directional derivative of f at the given angle

  1. #1
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    Find the directional derivative of f at the given angle

    Find the directional derivative of f at the given point in the direction indicated by the angle θ.
    f(x, y) = x sin(xy), (3, 0), θ = π/4
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  2. #2
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    If you look in any textbook you'll find a proof (or atleast a justification) for this

    the directional derivative of a function is given by

     \nabla f \cdot \mathbf{n}

    where n is a unit vector in the direction that your taking the derivative. And grad f is evaluated at the specified point.

    in this case it would be  \mathbf{n}=\frac{1}{\sqrt{2}} \begin{pmatrix} 1 \\ 1 \end{pmatrix}
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