Math Problem Statement

the equation, f(x, y) = x^2 - 3y + 30. Hessian Matrix: H(x, y) = \being{bmatrix} f_{xx} & f_{xy}\ f_{yx} & f_{yy}\end{bmatrix. If H(x, y) < 0, saddle point, H(x, y) > 0, turning point, if it is a turning point, if f_{xx} > 0, miminumum tunring point, f_{xx} < 0, maximum turning point. Identify each turning point of the equation.

Solution

The equation f(x,y)=x23y+30f(x, y) = x^2 - 3y + 30 needs to be analyzed for its turning points, minimum, maximum, or saddle points using the Hessian matrix. Let’s follow the steps systematically:

1. First-Order Partial Derivatives

The first-order partial derivatives are: fx=fx=2x,fy=fy=3.f_x = \frac{\partial f}{\partial x} = 2x, \quad f_y = \frac{\partial f}{\partial y} = -3.

The critical points occur where fx=0f_x = 0 and fy=0f_y = 0: 2x = 0 \quad \Rightarrow \quad x = 0, \quad -3 = 0 \quad \Rightarrow \quad \text{No solution for y}. Thus, the function has no critical points because fy=3f_y = -3 is constant and cannot equal zero.

2. Second-Order Partial Derivatives (Hessian Matrix Components)

The second-order partial derivatives are:

f_{yy} = \frac{\partial^2 f}{\partial y^2} = 0, \quad f_{xy} = f_{yx} = 0.$$ The Hessian matrix is: $$H(x, y) = \begin{bmatrix} f_{xx} & f_{xy} \\ f_{yx} & f_{yy} \end{bmatrix} = \begin{bmatrix} 2 & 0 \\ 0 & 0 \end{bmatrix}.$$ ### 3. Determinant of the Hessian The determinant of $$H(x, y)$$ is: $$\text{det}(H) = f_{xx}f_{yy} - (f_{xy})^2 = (2)(0) - (0)^2 = 0.$$ ### 4. Analysis of the Results - Since $$\text{det}(H) = 0$$, the Hessian test is inconclusive. This implies the nature of the point is indeterminate using only the Hessian determinant. - However, based on $$f_{xx} = 2 > 0$$, the function is convex in the $$x$$-direction, and no critical points satisfy both $$f_x = 0$$ and $$f_y = 0$$. Thus, we cannot identify a specific turning point. ### Conclusion The function $$f(x, y) = x^2 - 3y + 30$$ has **no critical points**. The absence of critical points precludes the identification of a minimum, maximum, or saddle point. --- Would you like further clarification or a deeper dive into the theoretical aspects? Here are some follow-up questions: 1. How is the determinant of the Hessian matrix related to the classification of critical points? 2. Why does the constant term $$-3y$$ prevent the existence of critical points in this case? 3. Can you provide another example where a Hessian determinant test is inconclusive? 4. How would the analysis change if $$f_y$$ were a function of $$y$$ instead of constant? 5. What does the convexity in the $$x$$-direction imply about the surface? **Tip:** If the Hessian determinant is zero, check the function's behavior in the region around the potential critical point for additional insights.

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Math Problem Analysis

Mathematical Concepts

Multivariable Calculus
Hessian Matrix
Critical Points Analysis

Formulas

First-order partial derivatives: f_x = ∂f/∂x, f_y = ∂f/∂y
Second-order partial derivatives: f_{xx} = ∂^2f/∂x^2, f_{yy} = ∂^2f/∂y^2, f_{xy} = f_{yx} = ∂^2f/∂x∂y
Hessian determinant: det(H) = f_{xx}f_{yy} - (f_{xy})^2

Theorems

Hessian determinant test for classifying critical points

Suitable Grade Level

Grades 11-12 or early college