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Math Help - Cartesian equation for a curve

  1. #1
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    Cartesian equation for a curve

    Hey guys i need help with this question for an assignment.

    Find a Cartesian equation for the curve and identify it:
    r = 2sin(θ) + 2cos(θ)

    i tried multipliying everything by r, getting:
    r^2 = 2rsin(θ) + 2rcos(θ)
    then making r^2 = x^2 + y^2 and making rsin(θ)=y and rcos(θ)=x.

    but that didn't work :/.

    please help
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  2. #2
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    Quote Originally Posted by CenturionMonkey View Post
    Hey guys i need help with this question for an assignment.

    Find a Cartesian equation for the curve and identify it:
    r = 2sin(θ) + 2cos(θ)

    i tried multipliying everything by r, getting:
    r^2 = 2rsin(θ) + 2rcos(θ)
    then making r^2 = x^2 + y^2 and making rsin(θ)=y and rcos(θ)=x.

    but that didn't work :/.

    please help
    sure it did, you just didn't finish ...

    r^2 = 2rsin(θ) + 2rcos(θ)

    x^2 + y^2 = 2y + 2x

    x^2 - 2x + y^2 - 2y = 0

    x^2 - 2x + 1 + y^2 - 2y + 1 = 2

    (x - 1)^2 + (y - 1)^2 = 2

    what's this an equation for?


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  3. #3
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    thanks, yeah it worked out actually the way i did it. Its just that for some reason my assignemt wouldn't accept the answer unless i factored out a y. :S.

    thanks anyway
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