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Math Help - area of surface of revolution about x-axis- two r's

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    Post surface area of revolution about x-axis

    Determine the area of the surface of revolution about the x-axis of the intersection between the curves r=sinx and r=cosx.


    I drew a picture and found they intersected at 0 and .5 and I know the equation is:
    S = \int_a^b {2\pi y\sqrt {1 + {{(\frac{{dy}}<br />
{{dx}})}^2}} dx}<br />

    but I don't know if b is .5 or pi/4

    and I tried this:
    S = \int {2\pi \cos x\sqrt {1 + {{( - \sin x)}^2}} dx - \int {2\pi (\sin x)\sqrt {1 + {{(\cos x)}^2}} dx} } <br />
    but I couldn't integrate it correctly
    Last edited by genlovesmusic09; December 6th 2009 at 04:20 PM.
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