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Math Help - parametric arc length

  1. #1
    Member
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    Jul 2009
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    parametric arc length

    Consider the parametric equation
    x=4(cos+sin)
    y=4(sincos)

    What is the length of the curve for =0 to =9pi/10

    the formula i believe is

    L=integral from t0 to t1 sqrt((dx/dt)^2+(dy/dt)^2)dt


    ive tried pluggin in the derivatives of of x and y for dx dt and integrating from 0 to 9pi/10 but its not working
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  2. #2
    Junior Member
    Joined
    Aug 2009
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    I think that is the correct formula. What is the problem? I get x'(\theta) = 4\,\theta\,\cos(\theta), ~y'(\theta) = 4\,\theta\,\sin(\theta). Gives an arc length of \frac{81 \pi^2}{50}, which looks plausible.
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