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    hi
    i cant seem to make head or tail of this question. here it goes;

    find the volume of the solid generated by rotating the area enclosed by the curve y= 2-x^2 and the line y = 1, about y=1.

    i am not sure how to start. can someone please explain?

    thanks
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    You need to put it in the form x=g(y). Because you're rotating it around the y-axis, rather than the x-axis, the formula becomes \displaystyle \int_a^b \pi x^2\, dy rather than \displaystyle \int_a^b \pi y^2\, dx as it is normally.
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    thanks. i will try this.
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    (Original post by aurao2003)
    thanks. i will try this.
    You're rotating about y=1 not the y axis.

    Did you sketch it?

    The volume you need is the same as the volume that results when you rotate the area between the x axis and y=1-x^2 about the x axis. Can you see why?
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    (Original post by nuodai)
    You need to put it in the form x=g(y). Because you're rotating it around the y-axis, rather than the x-axis, the formula becomes \displaystyle \int_a^b \pi x^2\, dy rather than \displaystyle \int_a^b \pi y^2\, dx as it is normally.
    Not often you slip up.

    (Original post by Get me off the £\?%!^@ computer)
    You're rotating about y=1 not the y axis.

    Did you sketch it?

    The volume you need is the same as the volume that results when you rotate the area between the x axis and y=1-x^2 about the x axis. Can you see why?
    I'd go with "Get me...."
 
 
 
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