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Math Help - Circle Problems

  1. #1
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    Circle Problems

    I seem to keep having trouble with parameterizations of circles, particularly thier direction i think,

    for instance for the quarter circle that goes anticlockwise from (0,2) to (-2,0) can someone explain to me how the parameterization is,


    c(t)= (-2sint , 2 cost)

    0 <= t<= pi/2

    I would have thought;

    x= rcost, y=rsint

    Therefore; c(t) = (2cost, 2sint)
    where pi/2 <= t <= pi

    Any explanation would be very helpful,

    Cheers,
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  2. #2
    Super Member Random Variable's Avatar
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    They're both correct.
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  3. #3
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    ok, well thats a relief that myne is correct, can you possibly explain to me how thiers works?

    As it was required to evaluate a double integral, and i seem to have trouble understanding the way they have gone about it,

    Many thanks
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  4. #4
    Super Member Random Variable's Avatar
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    Quote Originally Posted by monster View Post
    ok, well thats a relief that myne is correct, can you possibly explain to me how thiers works?

    As it was required to evaluate a double integral, and i seem to have trouble understanding the way they have gone about it,

    Many thanks
     \big(-2 \sin(0), 2 \cos(0)\big) = (0,2) = \big(2\cos(\pi /2), 2\sin(\pi/2)\big)

     \big(-2 \sin(\pi /2), 2 \cos(\pi /2)\big) = (-2,0) = \big(2\cos(\pi), 2\sin(\pi)\big)


    It doesn't matter which parametrization you use.
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