2.3.6 (HL)—Surplus calculations

Surplus can be calculated as geometric areas: triangle area is one-half × base × height, using the relevant price and quantity differences.

The diagram must identify intercepts, equilibrium and the actual price; a policy can transfer surplus or create deadweight loss.

Label axes and vertices, calculate each area, then compare total and distributional change.

A consumer-surplus triangle with base 100 units and height $4 has area$200.

Do not use a rectangle when the demand or supply boundary is sloped.