Understanding A = 4πr²
The total area covering a sphere is calculated using A = 4πr². This means the surface of any sphere is exactly four times the area of its circular equatorial cross-section.
Worked Example
Find the surface area of a weather balloon with a radius of 2.1 meters.
Formula: A = 4 × π × (2.1)²
2.1² = 4.41 m²
A = 4 × 3.14159 × 4.41 ≈ 55.42 square meters.