Key Idea: Topic 2.3 shows how demand and supply interact to determine the market price and quantity, what happens when equilibrium changes, and how to measure consumer and producer surplus.
✅ Core definitions
⚖️ Surplus and shortage
📊 How equilibrium changes
Memory trick: D shifts → P and Q move in the same direction. S shifts → P and Q move in opposite directions.
🔀 Simultaneous shifts
Always draw the diagram step by step: original equilibrium → shift one curve → shift the other → identify what is certain and what is indeterminate.