What are the critical points of a function with multiple variables?

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Homework Help Overview

The discussion revolves around finding the critical points of a function of two variables, specifically f(x,y) = 2x^3 + xy^2 + 5x^2 + y^2 + 100. Participants express uncertainty regarding the implications of the x^3 term in the function and how it affects the process of finding critical points.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the need to set the partial derivatives of the function to zero to find critical points. There are questions about how to handle the quadratic nature of the partial derivatives and concerns about the complexity introduced by the x^3 term.

Discussion Status

Some participants have offered guidance on setting the components of the partial derivatives to zero, while others are questioning the interpretation of the derivatives and the nature of critical points. Multiple interpretations of the problem are being explored, and there is an ongoing exchange of ideas without a clear consensus.

Contextual Notes

Participants are grappling with the definitions and implications of critical points, particularly in relation to the behavior of the function's derivatives. There is a mention of confusion regarding whether critical points are defined solely by the first derivatives being zero or if other conditions apply.

Chadlee88
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Homework Statement


Find all the critical points of f(x,y) = 2x^3+xy^2+5x^2+y^2+100

Homework Equations





The Attempt at a Solution



I'm really not sure how to do this question due the the x^3 term in the function. Could someone please advise how to start this.

Thanx :D
 
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The critical points are where the partial derivatives of f with respect to x and y vanish simultaneously. Why should the x^3 be a problem?
 
Partial derivatives

(6x^2+y^2+10x)i + (2xy+2y)j

how am i supposed to find values of x and y that make it equal to zero??

the partial derivative with respect to x is a quadratic function with both x and y terms. so I'm stuck!
 
Chadlee88 said:
Partial derivatives

(6x^2+y^2+10x)i + (2xy+2y)j

how am i supposed to find values of x and y that make it equal to zero??

the partial derivative with respect to x is a quadratic function with both x and y terms. so I'm stuck!

You have two components and you can set each to zero. Then you have two equations and two unknowns.
 
You shouldn't really have components anyway. The partial derivatives aren't a vector. Start with the second one 2xy+2y=0.
 
Arent critical points those where either first derivative is 0 or not defined ?
 
Dick said:
You shouldn't really have components anyway. The partial derivatives aren't a vector. Start with the second one 2xy+2y=0.

good point.
 

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