Answer: πr².
- A 2πr
- B πr²
- C πr³
- D 2πr²
Correct answer: B. πr²
Explanation: Area of circle = πr². Circumference = 2πr.
Three standard 3D solids and their key formulas: a cylinder's volume scales with the full height, a cone's volume is exactly one-third of the cylinder with the same base and height, and a sphere's volume and surface area both follow distinct r-based formulas worth memorising separately.
Concept context
Perimeters, areas, and volumes of 2D and 3D shapes