FoundBread
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- Aug 1, 2018
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Hi I'm having trouble with this Lagrange Multiplier problem. I've done a few other problems no problem but this one I can't wrap my head around at all.
(b) The equation of a general ellipsoid centred at the origin is
. . . . .\(\displaystyle \dfrac{x^2}{a^2}\, +\, \dfrac{y^2}{b^2}\, +\, \dfrac{z^2}{c^2}\, =\, 1\)
for \(\displaystyle a,\, b,\, c\, \in\, (0,\, \infty).\) Its volume is \(\displaystyle \frac{4}{3}\pi abc.\) Let \(\displaystyle L\) be a fixed positive constant.
Given the constraint \(\displaystyle a\, +\, b\, +\, c\, =\, L,\) show that the ellipsoid with greatest volume is a sphere.
I have the method:
f(x,y,z) is the function trying to get the max/min of it
g(x,y,z)=k is my constraint
and then I have f(x,y,z) - λ(g(x,y,z)-k)
and get the derivatives with relation to x,y,z,λ (presume it will be a,b,c,λ in my case)
Then let all them = 0 and sub my solutions into f.
But I really just am getting so stuck I'm not sure how to show a sphere is the best shape for it.
Any help would be greatly appreciated even just tips not looking for someone to do it for me. (It's from a former exam paper I'm studying for repeats)
Thanks
(b) The equation of a general ellipsoid centred at the origin is
. . . . .\(\displaystyle \dfrac{x^2}{a^2}\, +\, \dfrac{y^2}{b^2}\, +\, \dfrac{z^2}{c^2}\, =\, 1\)
for \(\displaystyle a,\, b,\, c\, \in\, (0,\, \infty).\) Its volume is \(\displaystyle \frac{4}{3}\pi abc.\) Let \(\displaystyle L\) be a fixed positive constant.
Given the constraint \(\displaystyle a\, +\, b\, +\, c\, =\, L,\) show that the ellipsoid with greatest volume is a sphere.
I have the method:
f(x,y,z) is the function trying to get the max/min of it
g(x,y,z)=k is my constraint
and then I have f(x,y,z) - λ(g(x,y,z)-k)
and get the derivatives with relation to x,y,z,λ (presume it will be a,b,c,λ in my case)
Then let all them = 0 and sub my solutions into f.
But I really just am getting so stuck I'm not sure how to show a sphere is the best shape for it.
Any help would be greatly appreciated even just tips not looking for someone to do it for me. (It's from a former exam paper I'm studying for repeats)
Thanks
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