Mathematics ACT Aspire Practice Test 2026 – Complete Study Resource

The area of a circle is defined using the formula πr², where "r" represents the radius of the circle. This formula derives from the geometric principles governing circles and relates to how the area is calculated based on the distance from the center of the circle to its outer edge.

In this formula, π (pi) is a mathematical constant approximately equal to 3.14159 and is essential for calculations involving circles. The area represents the amount of space contained within the circle. Since the area grows as the radius increases, squaring the radius (r²) reflects that growth rate, showing that if the radius doubles, the area increases by a factor of four, since (2r)² = 4r².

Other formulas listed, such as 2πr and πd, pertain to the circumference of the circle rather than its area. The term r² alone does not incorporate the necessary mathematical constant π, making it incomplete for defining the area. Thus, πr² accurately captures the relationship between the radius of a circle and the space enclosed within it.