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optimization headache

Name: Anonymous 2007-11-14 21:07

ok so i have a cone with a surface area of 2 but thats all i know, so know i have to find what the maximum volume i can have with that cone, so before i take the derivitive and set it to 0 I need either radius in terms of height or height in terms of radius and i know surface area = pi*r*sqrt(r^2+h^2) but im having a hell of a time getting one in terms of the other, any help?

Name: Anonymous 2007-11-15 4:57

>>2
Down here in Aus it's the end of the year.

>>1
2 = πr2√(r2+h2)

1. Divide both sides by πr2
2. Square both sides
3. Get h2 in terms of r
4. Root both sides, take the positive as h must be positive. You now have h in terms of r
5. V = 1/3πr2h
6. Substitute h from 4 into 5
7. Diffrentiate to get dV/dr. Use the product and chain rules or a calulator.
8. Let dV/dr = 0
9. Solve for r or graph it and get the r intercepts. Take the positive as r must be positive.
10. Substitute r back into the original eqation to gt h.
DONE

It's a bit long but easily doable.

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