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# Pure core 3 Watch

1. For 6aii on this paper:
http://www.mrbartonmaths.com/resourc...20core%203.pdf

I found the volume of revolution using 2pi but the mark scheme says only to use pi. Is this because the values of x and all to the power of 2, and you need to halve the overall answer to account for the symmetry in the graph?
2. (Original post by pippabethan)
For 6aii on this paper:
http://www.mrbartonmaths.com/resourc...20core%203.pdf

I found the volume of revolution using 2pi but the mark scheme says only to use pi. Is this because the values of x and all to the power of 2, and you need to halve the overall answer to account for the symmetry in the graph?
Nope, that's because of the definition of volume of revolution, if you look it up in your textbook, you'll see that the volume generated by a curve rotated 360 degrees around the x-axis is: . It's a common mistake to use instead of .
3. (Original post by Zacken)
Nope, that's because of the definition of volume of revolution, if you look it up in your textbook, you'll see that the volume generated by a curve rotated 360 degrees around the x-axis is: . It's a common mistake to use instead of .
Oh okay, I must've forgotten! Thank you for clearing this up
4. (Original post by pippabethan)
Oh okay, I must've forgotten! Thank you for clearing this up
No problem!

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