Which symbol is used to denote the constant in the circle area formula?

• A. Pi
• B. e
• C. i
• D. phi

Answer: (A)

The circle area formula uses a fixed constant that links radius to area. In A = π r^2, the symbol π (pi) is that constant. It represents the ratio of a circle’s circumference to its diameter and is the same for every circle, so it scales the area consistently with the radius. The other constants—e, i, and phi—belong to different areas of math (growth and logarithms, the imaginary unit, and the golden ratio, respectively) and don't appear in the standard circle area expression. So the symbol used is π.