Find the local minima, local maxima, and saddle points for the following function: f (x, y) = 6x² – 2x³ + 3y² + 6xy

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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### Finding Critical Points of a Multivariable Function

#### Problem Statement:
Find the local minima, local maxima, and saddle points for the following function:

\[ f(x, y) = 6x^2 - 2x^3 + 3y^2 + 6xy \]

#### Solution Outline:
To find the local minima, maxima, and saddle points, we follow these steps:

1. **Compute the First Derivatives:**
   - Find \( \frac{\partial f}{\partial x} \) and \( \frac{\partial f}{\partial y} \).

2. **Set First Derivatives to Zero:**
   - Solve the equations \( \frac{\partial f}{\partial x} = 0 \) and \( \frac{\partial f}{\partial y} = 0 \) to find critical points.

3. **Compute the Second Derivatives:**
   - Find \( \frac{\partial^2 f}{\partial x^2} \), \( \frac{\partial^2 f}{\partial y^2} \), and \( \frac{\partial^2 f}{\partial x \partial y} \).

4. **Apply the Second Derivative Test:**
   - Use the second derivatives to create the Hessian matrix.
   - Calculate the determinant of the Hessian to determine the nature of each critical point:
     - If \( D > 0 \) and \( \frac{\partial^2 f}{\partial x^2} > 0 \), it's a local minimum.
     - If \( D > 0 \) and \( \frac{\partial^2 f}{\partial x^2} < 0 \), it's a local maximum.
     - If \( D < 0 \), it's a saddle point.
     - If \( D = 0 \), the test is inconclusive.

This systematic approach will identify all salient features of the function's graph in the neighborhood of its critical points.
Transcribed Image Text:### Finding Critical Points of a Multivariable Function #### Problem Statement: Find the local minima, local maxima, and saddle points for the following function: \[ f(x, y) = 6x^2 - 2x^3 + 3y^2 + 6xy \] #### Solution Outline: To find the local minima, maxima, and saddle points, we follow these steps: 1. **Compute the First Derivatives:** - Find \( \frac{\partial f}{\partial x} \) and \( \frac{\partial f}{\partial y} \). 2. **Set First Derivatives to Zero:** - Solve the equations \( \frac{\partial f}{\partial x} = 0 \) and \( \frac{\partial f}{\partial y} = 0 \) to find critical points. 3. **Compute the Second Derivatives:** - Find \( \frac{\partial^2 f}{\partial x^2} \), \( \frac{\partial^2 f}{\partial y^2} \), and \( \frac{\partial^2 f}{\partial x \partial y} \). 4. **Apply the Second Derivative Test:** - Use the second derivatives to create the Hessian matrix. - Calculate the determinant of the Hessian to determine the nature of each critical point: - If \( D > 0 \) and \( \frac{\partial^2 f}{\partial x^2} > 0 \), it's a local minimum. - If \( D > 0 \) and \( \frac{\partial^2 f}{\partial x^2} < 0 \), it's a local maximum. - If \( D < 0 \), it's a saddle point. - If \( D = 0 \), the test is inconclusive. This systematic approach will identify all salient features of the function's graph in the neighborhood of its critical points.
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