Math Problem Statement

Suppose that f(x, y) = 5x + 2y at which -3 ≤ x ≤ 3, -3 ≤ y ≤ 3. Find the absolute minimum and maximum of f(x, y).

Solution

We are asked to find the absolute minimum and maximum values of the function f(x,y)=5x+2yf(x, y) = 5x + 2y on the closed region where 3x3-3 \leq x \leq 3 and 3y3-3 \leq y \leq 3.

Step-by-Step Approach:

  1. The function f(x,y)=5x+2yf(x, y) = 5x + 2y is linear, meaning that it doesn't have any critical points inside the region (since the partial derivatives don't depend on xx or yy). This implies the extreme values will occur on the boundary of the region.

  2. Evaluating the function at the corner points of the region:
    Since we are looking at the boundary values, let's calculate f(x,y)f(x, y) at the four corners of the rectangle given by the inequalities:

    • (3,3)(-3, -3)
    • (3,3)(-3, 3)
    • (3,3)(3, -3)
    • (3,3)(3, 3)

    Calculating these: f(3,3)=5(3)+2(3)=156=21f(-3, -3) = 5(-3) + 2(-3) = -15 - 6 = -21 f(3,3)=5(3)+2(3)=15+6=9f(-3, 3) = 5(-3) + 2(3) = -15 + 6 = -9 f(3,3)=5(3)+2(3)=156=9f(3, -3) = 5(3) + 2(-3) = 15 - 6 = 9 f(3,3)=5(3)+2(3)=15+6=21f(3, 3) = 5(3) + 2(3) = 15 + 6 = 21

  3. Conclusion:

    • The absolute minimum value of f(x,y)f(x, y) occurs at (3,3)(-3, -3), and it is 21-21.
    • The absolute maximum value of f(x,y)f(x, y) occurs at (3,3)(3, 3), and it is 2121.

Thus, the absolute minimum is 21-21 and the absolute maximum is 2121.


Would you like further details on this solution or have any other questions?

Here are 5 related questions for more practice:

  1. How do we find critical points for a non-linear function in two variables?
  2. How would the solution change if the function had x2x^2 or y2y^2 terms?
  3. Can a linear function have an absolute maximum or minimum inside the domain rather than on the boundary?
  4. How does the shape of the region affect where the extrema are found?
  5. What would happen if the boundary was a circle rather than a rectangle?

Tip: Always check the boundaries when solving optimization problems on a closed region!

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Math Problem Analysis

Mathematical Concepts

Multivariable Calculus
Optimization
Linear Functions

Formulas

f(x, y) = 5x + 2y

Theorems

Extreme Value Theorem

Suitable Grade Level

Grades 10-12