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Unformatted text preview: Lagrange Multipliers Jonathan L.F. King University of Florida, Gainesville FL 326112082, USA squash@ufl.edu Webpage http://www.math.ufl.edu/ squash/ 9 November, 2011 (at 23:44 ) Cubicsurface Problem On R 3 , find all extreme points P = ( x,y,z ) of function ( P ) := x 2 + y 2 + z 2 , subject to the two constraints that x y z = 54 ; ( a cubic surface ) C f : x + y + z = 12 . ( a plane ) C g : A picture. Note that the objective fnc and the two constraints are symmetric under all permuta tions of x,y,z . Thus our set of Lagrange points must have a sixfold ( 6 = 3! ) symmetry. A good picture suggests that the only Lagrange pts have some two of x,y,z equal. In the case that x = z , say, a picture suggests that there are 3 so lutions; two solns where the common value is pos itive and one soln with it negative. Thus the z = y , y = x and x = z solutions would give us 9 Lagrange pts all together, but only 3 types of Lagrangept. A solution Define specifier functions f ( P ) := x y z and g ( P ) := x + y + z , so that locus ( C f ) is some levelset of f , and lo cus ( C g ) is some levelset of g ....
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 Fall '07
 JURY
 Math, Calculus

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