Answer: x² + y² = 25.
- A x² + y² = 25
- B x² + y² = 5
- C x² − y² = 25
- D x + y = 5
Correct answer: A. x² + y² = 25
Explanation: A circle of radius r centred at the origin is x² + y² = r², so x² + y² = 25.
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