<p>Sorry for the bother but math is totally foreign to me. I am hoping to test out of it with the ap exam. Anyways, can anyone help me with this problem about volume of the revolution?</p>
<p>y=x^2, y=4 rotated around x=3.<br>
I got 68.333 but thats not the right answer and I figure out what I did wrong.
and</p>
<p>y=2x^2, y=x^2+9 rotated around the y axis. </p>
<p>thanks.</p>
<p>first problem: shell method
dV = 2pi<em>r</em>h<em>dr=2pi</em>(3 - x)<em>(4 - x^2)</em>dx
integrate from x = -2 to x = 2</p>
<p>second problem: shell method
dV = 2pi<em>r</em>h<em>dr=2pi</em>x<em>(x^2 + 9 - 2x^2)</em>dx
integrate from x = 0 to x = 3</p>
<p>hope this helps</p>
<p>210.06 for the first and 127.234 for the second. im prob wrong because its late and im tired as hellll</p>
<p>or try his/her way</p>
<p>thanks. I found out what I did wrong. I kept forgeting the 2 in 2pi near the end. argh!</p>
<p>it happens to all of us...my problem is that I always mess up signs...I've read over my work before and seen signs mysteriously switch lol</p>
<p>haha yes exactly my teacher used to love making fun of me because i would get owned with signs.</p>