Answer: √(r² - d²).
- A r - d
- B √(r² - d²)
- C r + d
- D √(r² + d²)
Correct answer: B. √(r² - d²)
Explanation: The centre O, the foot of perpendicular F (at distance d), and any point P on the cross-section circle form a right triangle. OP=r (radius), OF=d, FP=cross-section radius. Pythagoras: FP=√(r²−d²). Ans: √(r²−d²).
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