Answer: π(R² - r²).
- A π(R+r)
- B π(R² - r²)
- C π(R-r)²
- D 2π(R-r)
Correct answer: B. π(R² - r²)
Explanation: Area of annulus = πR² - πr² = π(R² - r²) = π(R+r)(R-r).
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