Multi-Variable Constrained Optimization using Partial Derivatives

00:00 10 marks

  • Exam Style - Paper 3
  • HL
  • Tier 4
  • Constrained optimization
  • Partial derivatives
  • Lagrange Multipliers
  • Multi-variable Calculus
  • Economic Implications of Optimization

A manufacturing company aims to minimize its production costs by optimally allocating resources for two raw materials, \(x\) and \(y\). The cost function is given by \(C(x,y)=4x^2 + 3y^2 + 5xy\), where \(x\) and \(y\) represent the quantities of material X and material Y, respectively, in suitable units.

The company initially operates under a production quota constraint that the total quantity of materials used must be exactly 100 units, represented by \(x + y = 100\).

Subsequently, due to new environmental regulations, an additional constraint is imposed, limiting the use of material Y relative to material X, specifically \(2x – y = 30\).

Solve the following:

(a) Determine the values of \(x\) and \(y\) that minimize the cost under the single production quota constraint \(x + y = 100\). Use the method of Lagrange multipliers.

(b) Find the optimal solution for the production costs when both the production quota \(x + y = 100\) and the environmental regulation \(2x – y = 30\) constraints are in effect.

(c) Discuss the impact of introducing the environmental regulation constraint on the optimization process. Interpret the economic implications of these constraints for the manufacturing company.

Part a

5 minutes 4 marks

Question

Determine the values of \(x\) and \(y\) that minimize the cost function \(C(x,y)=4x^2+3y^2+5xy\) under the constraint \(x+y=100\) using the method of Lagrange multipliers.



Hint Hint

Hint

Set up the Lagrange function \(L(x,y,\lambda)=4x^2+3y^2+5xy-\lambda(x+y-100)\) and find the partial derivatives with respect to \(x\), \(y\), and \(\lambda\).

  • Answer Answer

Complete Answer

The optimal solution is \(x=25\) and \(y=75\).

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Part b

5 minutes 4 marks

Question

Find the new optimal solution for \(C(x,y)=4x^2+3y^2+5xy\) when subjected to both constraints: \(x+y=100\) and \(2x-y=30\).



Hint Hint

Hint

With multiple constraints, first determine if a feasible region exists by solving the system of constraint equations. If a unique solution exists, that is the constrained optimum.

  • Answer Answer

Complete Answer

The optimal solution under both constraints is \(x=\frac{130}{3}\) and \(y=\frac{170}{3}\).

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Part c

4 minutes 2 marks

Question

Discuss the impact of introducing the environmental regulation constraint \(2x – y = 30\) on the optimization process and interpret the potential economic implications for the manufacturing company.



Hint Hint

Hint

Consider how the additional constraint affects the feasible region and the resulting production costs. Think about the economic trade-offs and strategic adjustments the company might need to make.

  • Answer Answer

Complete Answer

Introducing the environmental regulation constraint reduces the feasible region from a line (under a single constraint) to a single point (under two constraints, assuming consistency). This new constraint forces the company to operate at a specific allocation of resources, which may deviate from the cost-minimizing solution found under only the production quota. Economically, this could mean increased production costs compared to the single-constraint scenario, as the company is now restricted by both production limits and environmental standards, potentially necessitating investments in cleaner or more efficient technologies or materials.

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