Math Problem Statement

i have a problem Give h1, h2, h3, w1, w2, w3 >= 0 h1w3 = 2 h2w1 = 4 h2w2 = 4 find minimum of h1w1 + h1w2 + h2w3 Can you solve with linear programming ?

Solution

Yes, this problem can be formulated and solved using linear programming. The goal is to minimize the expression h1w1+h1w2+h2w3h_1w_1 + h_1w_2 + h_2w_3 given the constraints:

  1. h1×w3=2h_1 \times w_3 = 2
  2. h2×w1=4h_2 \times w_1 = 4
  3. h2×w2=4h_2 \times w_2 = 4
  4. h1,h2,h3,w1,w2,w30h_1, h_2, h_3, w_1, w_2, w_3 \geq 0

Steps to Solve the Problem:

  1. Define the Objective Function: Minimize Z=h1w1+h1w2+h2w3\text{Minimize } Z = h_1w_1 + h_1w_2 + h_2w_3

  2. Constraints: h1×w3=2(Constraint 1)h_1 \times w_3 = 2 \quad \text{(Constraint 1)} h2×w1=4(Constraint 2)h_2 \times w_1 = 4 \quad \text{(Constraint 2)} h2×w2=4(Constraint 3)h_2 \times w_2 = 4 \quad \text{(Constraint 3)} h1,h2,h3,w1,w2,w30h_1, h_2, h_3, w_1, w_2, w_3 \geq 0

  3. Substitute the Constraints into the Objective Function: From constraint 1: w3=2h1w_3 = \frac{2}{h_1}
    From constraint 2: w1=4h2w_1 = \frac{4}{h_2}
    From constraint 3: w2=4h2w_2 = \frac{4}{h_2}

    The objective function becomes: Z=h1(4h2)+h1(4h2)+h2(2h1)Z = h_1\left(\frac{4}{h_2}\right) + h_1\left(\frac{4}{h_2}\right) + h_2\left(\frac{2}{h_1}\right) Simplifying: Z=8h1h2+2h2h1Z = \frac{8h_1}{h_2} + \frac{2h_2}{h_1}

  4. Optimization: To find the minimum value, we differentiate ZZ with respect to h1h_1 and h2h_2, set the derivatives to zero, and solve for the optimal values of h1h_1 and h2h_2.

Solution via Substitution:

The expression Z=8h1h2+2h2h1Z = \frac{8h_1}{h_2} + \frac{2h_2}{h_1} is not linear, but it can be minimized by recognizing it's a convex function in terms of h1h_1 and h2h_2. We use the symmetry or AM-GM inequality to find the minimum.

Using the AM-GM inequality: 8h1h2+2h2h12(8h1h2)(2h2h1)=216=8\frac{8h_1}{h_2} + \frac{2h_2}{h_1} \geq 2\sqrt{ \left(\frac{8h_1}{h_2}\right)\left(\frac{2h_2}{h_1}\right)} = 2\sqrt{16} = 8

The equality holds when: 8h1h2=2h2h1\frac{8h_1}{h_2} = \frac{2h_2}{h_1}

Solving this gives: h22=4h12h_2^2 = 4h_1^2

So h2=2h1h_2 = 2h_1.

Using the constraints, substitute h2=2h1h_2 = 2h_1 into h2×w1=4h_2 \times w_1 = 4: 2h1×w1=4w1=2h12h_1 \times w_1 = 4 \Rightarrow w_1 = \frac{2}{h_1} Similarly, for w2w_2: w2=2h1w_2 = \frac{2}{h_1}

Finally, w3=2h1w_3 = \frac{2}{h_1}, and the expression for ZZ becomes: Z=8h12h1+2(2h1)h1=4+4=8Z = \frac{8h_1}{2h_1} + \frac{2(2h_1)}{h_1} = 4 + 4 = 8

So, the minimum value of ZZ is 8.

Conclusion:

The minimum value of h1w1+h1w2+h2w3h_1w_1 + h_1w_2 + h_2w_3 is 8\boxed{8}.

Would you like more details or have any questions?


Here are five related questions:

  1. How does the AM-GM inequality help in optimizing non-linear functions?
  2. What other methods can be used to minimize a non-linear function like 8h1h2+2h2h1\frac{8h_1}{h_2} + \frac{2h_2}{h_1}?
  3. Can this problem be generalized for more complex systems?
  4. How do we know the function Z=8h1h2+2h2h1Z = \frac{8h_1}{h_2} + \frac{2h_2}{h_1} is convex?
  5. What role does substitution play in solving optimization problems?

Tip: When dealing with constraints, always check if substituting them into the objective function simplifies the problem before proceeding to more complex methods.

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Math Problem Analysis

Mathematical Concepts

Linear Programming
Optimization

Formulas

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Theorems

AM-GM Inequality

Suitable Grade Level

Advanced Mathematics