Answer: a/√3.
- A a/√3
- B a/√2
- C a/√3 × 2
- D a√3/3 = a/√3
Correct answer: A. a/√3
Explanation: For equilateral triangle: R = a/√3. (Using R = abc/(4×Area) = a³/(4 × √3a²/4) = a/√3).
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