Find all the local maxima, local minima, and saddle points of the function. f(x,y) = − 3x² - 7xy - 8y² + 3x +27y+9

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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**Problem Statement:**

Find all the local maxima, local minima, and saddle points of the function.

**Function:**

\[ f(x, y) = -3x^2 - 7xy - 8y^2 + 3x + 27y + 9 \]

**Explanation:**

This problem involves identifying critical points of a given function of two variables, \(f(x, y)\). Critical points occur where the first derivatives of the function with respect to each variable are zero. These points can be classified as local maxima, local minima, or saddle points by analyzing the second derivatives or using the Hessian matrix.
Transcribed Image Text:**Problem Statement:** Find all the local maxima, local minima, and saddle points of the function. **Function:** \[ f(x, y) = -3x^2 - 7xy - 8y^2 + 3x + 27y + 9 \] **Explanation:** This problem involves identifying critical points of a given function of two variables, \(f(x, y)\). Critical points occur where the first derivatives of the function with respect to each variable are zero. These points can be classified as local maxima, local minima, or saddle points by analyzing the second derivatives or using the Hessian matrix.
Expert Solution
Step 1

Consider a multivariable function fx,y such that its first and second order partial derivatives exist and are continuous. Then the point a,b is said to be a critical point of the function if it satisfies the partial differential equations fxa,b=0 and fya,b=0. Define an equation D=fxxa,bfyya,b-fxya,b2. Then,

  • If D>0 and fxxa,b>0 then a,b is a point of local minimum.
  • If D>0 and fxxa,b<0 then a,b is a point of local maximum.
  • If D<0 then a,b is a saddle point.
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