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# Volume/surface area of a sphere watch

1. OK, so I was working out what the formula for the surface area + volume of a torus would be and I got both right. Then I thought 'right, applying a similar principle to a sphere should work too'.

So this is what happened:
VOLUME
A sphere is basically a semicircle rotated around an axis. (works for a full circle too).
It is rotated for the length of the full circle's circumference.

And this is what I got..
volume = 1/2.pi.r^2.2.pi.r
= pi^2.r^3
SURFACE AREA
Using the semicircle-around-an-axis idea again;
surface area = 2.pi.r.pi.r = 2.pi^2.r^2

... which is certainly not what it was supposed to be.

So why doesn't this method work? What have I done wrong?
This is probably a stupid question
2. Aha, never mind! I have to use the centroid of the semicircle rather than the radius... laziness does not pay of...

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Updated: November 3, 2013
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