How do I find the critical points of this multivariable function?

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SUMMARY

The discussion focuses on finding critical points of the multivariable function defined as f(x, y) = x4 + 4xy + y4. The user calculated the partial derivatives, resulting in f'x = 4x3 - 4y and f'y = 4y3 - 4x. Setting these derivatives to zero led to the realization that y = x3 and x = y3 represent an infinite set of critical points, prompting confusion regarding their uniqueness. The user ultimately clarified that these equations are not equivalent, indicating a misunderstanding in their interpretation of critical points.

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  • Learn about the second derivative test for classifying critical points
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Homework Statement


The function is defined in the xy-plane. Find all critical points and determine their characteristics.


Homework Equations


f(x, y) = x4 + 4xy + y4


The Attempt at a Solution


I tried finding the partial derivatives.
f'x = 4x3 - 4y
f'y = 4y3 - 4x
Setting them to 0 gives y = x3.
If x = 1, y = 1, if x = 2, y = 8, etc.
This means that there's an infinite amount of critical points, this can't be right?
 
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Nevermind, my brain is kinda tired... just realized that x = y^3 and y = x^3 is not the same equation. Well thanks anyway :).
 

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