Optimizing a Constrained Two-variable Cost Function

00:00 9 marks

  • Exam Style - Paper 2
  • SL & HL
  • Tier 4
  • Derivatives
  • Optimization
  • Two-variable functions
  • Constraint substitution

A company produces two products, x and y, and the cost associated with producing these is modeled by the function \(C(x, y) = x^2 + 2y^2 – 4x – 8y + 20\). Due to resource constraints, the total production is fixed so that \(y = 10 – x\).

(a) Express the cost function solely in terms of \(x\) by substituting the constraint.

(b) Differentiate the resulting function to find the critical point. Determine the value of \(x\) that minimizes the cost and compute the corresponding minimum cost.

(c) Interpret the result in the context of production optimization, explaining what the optimal production quantities imply.

Part a

4 minutes 3 marks

Question

Substitute \(y = 10 – x\) into the cost function \(C(x, y) = x^2 + 2y^2 – 4x – 8y + 20\) to express it solely in terms of \(x\). Simplify your answer.



Hint Hint

Hint

Substitute the constraint carefully and expand the squared term correctly.

  • Answer Answer

Complete Answer

\(C(x) = 3x^2 – 36x + 140\)

  • Mark Scheme Mark Scheme
  • Answer Explanation Answer Explanation

Part b

4 minutes 3 marks

Question

Differentiate the function \(C(x) = 3x^2 – 36x + 140\) to find its critical point. Determine the value of \(x\) that minimizes the cost and compute the minimum cost.



Hint Hint

Hint

Differentiate \(C(x)\) and set the derivative equal to zero to solve for \(x\).

  • Answer Answer

Complete Answer

\(x = 6, \; C(6) = 32\)

  • Mark Scheme Mark Scheme
  • Answer Explanation Answer Explanation

Part c

4 minutes 3 marks

Question

Interpret the results from parts (a) and (b) in the context of production optimization. Explain what the optimal values indicate about the production quantities of products x and y.



Hint Hint

Hint

Relate the value of \(x\) and the constraint \(y = 10-x\) to the optimal production quantities.

  • Answer Answer

Complete Answer

Optimal production is achieved when \(x = 6\) and \(y = 4\), meaning that producing 6 units of product x and 4 units of product y minimizes the cost.

  • Mark Scheme Mark Scheme
  • Answer Explanation Answer Explanation

Math Editor

Report Question


Please enter keywords