Area of a circle

The area of a circle measures the space enclosed within it. Unlike circumference, the area formula uses the radius squared. **The Formula:** A = πr² (Area = pi × radius × radius) **Important Notes:** - You must use the RADIUS, not the diameter - If given diameter, divide by 2 first to get radius - r² means r × r, not r × 2 **Step-by-Step Method:** 1. Identify the radius (or calculate from diameter) 2. Square the radius (r × r) 3. Multiply by π 4. Round if required and include units² **Working with Diameter:** If given diameter d: A = π × (d/2)² = πd²/4 **Reverse Problems:** Given area, find radius: r = √(A/π) Given area, find diameter: d = 2√(A/π) **Units:** - If radius is in cm, area is in cm² - If radius is in m, area is in m² - Always include the squared unit **Semicircles and Sectors:** - Semicircle area = ½ × πr² - Quarter circle area = ¼ × πr² - Sector area = (angle/360) × πr² **Exam Tips:** - Always use radius, not diameter - Check if answer should be in terms of π or as a decimal - Square before multiplying by π - Remember to square the units too