Directional derivative

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"Find the directional derivative fu(1,2) for the function f with u = (3i-4j)/5 for f(x,y)= x^(2) - y^(2)."

Thank you!

  • Directional derivative -

    df(x,y)/dx = 2x
    df(1,2)/dx = 2
    df(x,y)/dy = -2y
    df(1,2)/dy = -4
    Directional derivative =
    = <2,-4> • <(3/5),-(4/5)>
    = (6/5) + (16/5)
    = 22/5

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