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Calculus Area between curves

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Sketch the region enclosed by the given curves. Decide whether to integrate with respect to x or y. Then find the area of the region.
3y+x=3 , y^2-x=1

  • Chris - Amy -Calculus Area between curves -

    Why are you switching names ??

    find the intersection;
    from the first:
    x = 3 - 3y

    into the 2nd:
    y^2 - (3-3y) = 1
    y^2 + 3y - 4 = 0
    (y+4)(y-1) = 0
    y = -4 or y = 1

    in x = 3-3y ....
    if y = 1, x = 0 ---->(0,1)
    if y = -4 , x = 15 , ---> (15, -4)

    Your sketch should look like this and my answers are confirmed
    http://www.wolframalpha.com/input/?i=plot+3y%2Bx%3D3+%2C+y%5E2-x%3D1

    judging from the graph I would integrate with respect to y
    so the effective width of my horizontal slice
    = 3-3y - (y^2 - 1)
    = 4 - 3y - y^2

    area = ∫(4 - 3y - y^2) dy from -4 to 1
    = (4y - (3/2)y^2 - (1/3)y^3) | from -4 to 1
    = (4 - 3/2 - 1/3) - (-16 -24 + 64/3)
    = 13/6 - (-56/3)
    = 125/6

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