Analyzing Critical Points of a Multivariable Function

In summary, given n ≥ 2, n ∈ ℵ and f(x,y) = a*x^n + c*y^n where a*c ≠ 0, there is only one critical point at (0,0). The criteria of the determinant of the hessian matrix cannot be used to determine the kind of critical point. However, considering the options of ac > 0 and ac < 0, it can be concluded that if n is even and ac > 0, the critical point is a minimum if a > 0 and a maximum if a < 0. If n is odd, the critical point is a saddle point. Similarly, if ac < 0 and n is even, the critical point is a saddle point
  • #1

pbialos

Given [tex]n\geq 2, n\in \aleph[/tex] and [tex]f(x,y)=a*x^n+c*y^n[/tex] where [tex]a*c\not=0[/tex], determine the nature of the critical points. I found the only critical point at (0,0) and when i tried to use the criteria of the determinant of the hessian matrix to determine the kind of critical point it was, it gave me 0, so i can`t say nothing by this criteria.
I don't know what kind of analysis of the function i am supposed to do, so any help would be much appreciated.

Many Thanks, Paul.
 
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  • #2
You can say something of the critical points. First, consider the options ac < 0 and ac > 0. If ac > 0, then you just have polynomials that are just positive multiples of each other. If the polynomial is of odd order, you have nothing (think f(x) = x³), and if it is of even order, then you have a minimum if a > 0 (and hence c > 0) or a maximum if a < 0 (and hence c < 0). Now if ac < 0, then if n is odd, then you again have nothing since this is the same if n is odd and ac > 0, just rotated by 90o. If n is even, then you'll have a saddle point of type (1-1) and unlike minima and maxima, an upside down saddle point is still a saddle point (whereas a maximum becomes a minimum).
 
  • #3


The analysis of critical points for a multivariable function involves determining the points where the partial derivatives of the function are equal to zero. In this case, the only critical point is (0,0) since both partial derivatives of f(x,y) with respect to x and y are equal to zero.

To determine the nature of this critical point, we can use the second derivative test or the Hessian matrix. However, in this case, the Hessian matrix is not helpful since its determinant is equal to zero. This means that the second derivative test does not provide any information about the nature of the critical point.

In order to further analyze the critical point at (0,0), we can look at the behavior of the function around this point. We can do this by plotting the function or by evaluating the function at points close to (0,0). This will help us determine if the critical point is a local maximum, local minimum, or a saddle point.

Additionally, we can also consider the behavior of the function along different paths approaching the critical point. This can give us a better understanding of the behavior of the function at this point.

In conclusion, while the Hessian matrix may not provide any information about the nature of the critical point, there are other methods we can use to analyze the function and determine the nature of the critical point at (0,0).
 

What is a multivariable function?

A multivariable function is a mathematical function that takes more than one input variable and produces a single output. It is commonly represented as f(x,y) or z = f(x,y).

What are critical points in a multivariable function?

Critical points in a multivariable function are points where all partial derivatives are equal to zero. They can be local maxima, local minima, or saddle points.

How do you find critical points in a multivariable function?

To find critical points, you need to take the partial derivative of the function with respect to each input variable and set them equal to zero. Then, you can solve the resulting system of equations to find the critical points.

Why are critical points important in analyzing a multivariable function?

Critical points are important because they can tell us about the behavior of the function. Local maxima and minima can indicate the presence of peaks and valleys, while saddle points can indicate a change in direction.

How can critical points be used to optimize a multivariable function?

By analyzing the critical points, we can determine the optimal values for the input variables that will produce the maximum or minimum output. This can be useful in a variety of fields such as engineering, economics, and physics.

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