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# volume of a solid Watch

1. 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
2. You need to put it in the form . Because you're rotating it around the y-axis, rather than the x-axis, the formula becomes rather than as it is normally.
3. thanks. i will try this.
4. (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?
5. (Original post by nuodai)
You need to put it in the form . Because you're rotating it around the y-axis, rather than the x-axis, the formula becomes rather than 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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