Classifying Critical Points of Multivariable Functions

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SUMMARY

The discussion focuses on finding and classifying the critical points of the multivariable function f(x,y,z) = xy + xz + yz + x^3 + y^3 + z^3. The first derivatives are calculated as df/dx = y + z + 3x^2, df/dy = x + z + 3y^2, and df/dz = x + y + 3z^2. The critical point (0,0,0) is identified, and participants suggest leveraging the symmetry of the function to find additional critical points by manipulating the derivatives.

PREREQUISITES
  • Understanding of multivariable calculus
  • Familiarity with gradient and critical points
  • Knowledge of symmetry in mathematical functions
  • Ability to compute partial derivatives
NEXT STEPS
  • Explore methods for classifying critical points in multivariable functions
  • Learn about the Hessian matrix and its role in determining local maxima and minima
  • Investigate the implications of symmetry in multivariable calculus problems
  • Practice finding critical points of other symmetric functions
USEFUL FOR

Students and educators in multivariable calculus, mathematicians analyzing critical points, and anyone interested in the application of symmetry in mathematical functions.

gassi
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Homework Statement



Find and classify the critical points of f(x,y,z) = xy + xz + yz + x^3 + y^3 + z^3

Homework Equations


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The Attempt at a Solution



df/dx = y + z +3x^2, df/dy = x + z + 3y^2 and df/dz = x + y + 3z^2

a point x is a critacal point if the gradient equals 0.

Obviously (0,0,0) is a critical point but I´m not sure how to find the others.
 
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gassi said:
Obviously (0,0,0) is a critical point but I´m not sure how to find the others.

Hi gassi! Welcome to PF! :smile:

Hint: the whole problem is completely symmetric in x y and z, isn't it?

So try adding or subtracting df/dx df/dy and df/dz. :smile:
 

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