Critical points, several variables

Click For Summary
SUMMARY

The critical points of the function f(x, y) = x³ + y³ + 3x² + 6y² - 9x + 9y + 1 are determined by solving the partial derivatives. The first derivative with respect to x, df/dx = 3x² + 6x - 9, yields critical points at x = -3 and x = 1. The first derivative with respect to y, df/dy = 3y² + 12y + 9, results in critical points at y = -3 and y = -1. The corresponding critical points in the xy-plane are (-3, -3), (-3, 1), (1, -3), and (1, 1).

PREREQUISITES
  • Understanding of partial derivatives
  • Familiarity with critical points in multivariable calculus
  • Knowledge of polynomial functions
  • Ability to solve quadratic equations
NEXT STEPS
  • Study the method of Lagrange multipliers for constrained optimization
  • Learn about the second derivative test for classifying critical points
  • Explore the implications of critical points in optimization problems
  • Investigate the behavior of multivariable functions using contour plots
USEFUL FOR

Students and professionals in mathematics, particularly those studying calculus and optimization, will benefit from this discussion. It is also useful for anyone looking to understand the process of finding critical points in multivariable functions.

simba_
Messages
19
Reaction score
0

Homework Statement


Find the critical points of

x3 + y3 + 3x2 + 6y2 - 9x + 9y +1

you do not need to define the critical points

Homework Equations





The Attempt at a Solution



i have
df/dx = 3x2 + 6x - 9 and when i solve this x = -3, 1
but i don't know what the corresponding y values are

df dy = 3y2 + 12y + 9 and so y = -3, -1
and here i don't know what the corresponding x values are
 
Physics news on Phys.org
simba_ said:

Homework Statement


Find the critical points of

x3 + y3 + 3x2 + 6y2 - 9x + 9y +1

you do not need to define the critical points

Homework Equations





The Attempt at a Solution



i have
df/dx = 3x2 + 6x - 9 and when i solve this x = -3, 1
but i don't know what the corresponding y values are

df dy = 3y2 + 12y + 9 and so y = -3, -1
and here i don't know what the corresponding x values are
fx = 0 when x = -3 or x = 1
fy = 0 when y = -3 or y = 1

So both partials are zero at (-3, -3), (-3, 1), (1, -3), and (1, 1).
 
tyty
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 16 ·
Replies
16
Views
3K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 9 ·
Replies
9
Views
4K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
3
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K