Lagrange multipliers and partial derivatives

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SUMMARY

The discussion focuses on using Lagrange multipliers to find the minimum point of the function 4x² + y² + z² subject to the constraint 2x + 3y + z - 11 = 0. The user sets up the function F = 4x² + y² + z² + λ(2x + 3y + z) and derives the partial derivatives df/dx, df/dy, and df/dz. The next steps involve setting these derivatives equal to zero, leading to a system of equations that can be solved by eliminating λ and incorporating the constraint equation.

PREREQUISITES
  • Understanding of Lagrange multipliers
  • Knowledge of partial derivatives
  • Familiarity with solving systems of equations
  • Basic algebraic manipulation skills
NEXT STEPS
  • Study the method of Lagrange multipliers in detail
  • Practice solving systems of equations involving multiple variables
  • Explore applications of partial derivatives in optimization problems
  • Learn about constraint optimization in multivariable calculus
USEFUL FOR

Students studying calculus, particularly those focusing on optimization techniques, as well as educators teaching multivariable calculus concepts.

phrygian
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Homework Statement



Find the point on 2x + 3y + z - 11 = 0 for which 4x^2 +y^2 +z^2 is a minimum

Homework Equations





The Attempt at a Solution



Using lagrange multipliers I find:

F = 4x^2 + y^2 + z^2 + l(2x + 3y + z)

Finding the partial derivatives I get the three equations:

df/dx = 8x + 2l
df/dy= 2y + 3l
df/dz= 2z + l

This is where I am stuck, what are the next steps for solving the system of equations?
 
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Well, first set them equal to 0! They are equivalent to [itex]x= -\lambda[/itex], [itex]2y/3-\lambda[/itex] and [itex]2z= -\lambda[/itex]. You can easily eliminate [itex]\lambda[/itex] by setting those equal to each other. And don't forget that you have 2x+ 3y+ z= 11 as a third equation.
 

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