Isocost and isoquant can be attributed to

1. Analyze the question The question asks which area of economics uses the tools called isocost and isoquant.

2. Explain the concepts

• Isoquant: a curve showing all the combinations of two inputs (e.g. labour and capital) that give the same level of output. "Iso" means equal and "quant" means quantity.
• Isocost: a line showing all the combinations of two inputs that a producer can buy for the same total cost, given the input prices.

A producer reaches the least-cost combination of inputs, which is the producer's equilibrium, where the isocost line is tangent to the isoquant.

3. Step-by-step solution

• Both tools deal with inputs (factors of production) and output.
• They help a firm decide how to combine labour and capital to produce efficiently.
• This is the subject matter of the theory of production.

Checking the other options:

• A. Theory of consumer behaviour: this uses indifference curves and budget lines. These are the consumer's counterparts of isoquants and isocost lines.
• B. Theory of cost: this deals with cost curves such as AC, MC and AVC. It is related, but isocost and isoquant are not its main tools.
• D. Theory of value: this deals with how prices and values of goods are determined.

4. Answer The correct option is C. Theory of production.

5. Exam tip Match the pairs:

• Indifference curve and budget line → consumer theory
• Isoquant and isocost → producer/production theory

Remember: "Iso-quant = output quantity", so it belongs to production.