The area of a circle with radius r is A = π r^2. Which option is correct for the area in terms of r?

• A. π r^2
• B. 2 π r
• C. π d^2
• D. 2 r

Answer: (A)

The key idea is that the area of a circle grows with the square of the radius. The formula A = π r^2 expresses exactly that: you take the radius, multiply it by itself, and multiply by π to get the area.

This matches the given relationship directly, so the area in terms of r is π r^2. The other forms refer to different quantities: 2π r is the circumference, the length around the circle; π d^2 would use the diameter and, since d = 2r, would equal 4π r^2, not A; and 2 r is just a length, not an area.