What is the formula for calculating the area of a circle?

The formula for calculating the area of a circle is A = πr², where A represents the area and r represents the radius of the circle. This formula derives from the geometric properties of circles, specifically relating the radius to the total space enclosed within the circle. The expression π (pi) is a constant approximately equal to 3.14159, which is used to relate the diameter of the circle to its circumference and area.

In this context, the other options represent different geometric formulas: one calculates the area of a trapezoid, incorporating the bases and height; another computes the circumference of a circle, which measures the distance around the circle; and the last represents the area of a rectangle or parallelogram, depending on the context of 'b' and 'h' designations. Each of these alternatives is relevant in their specific contexts, but they do not apply to finding the area of a circle. Thus, the formula A = πr² is specifically tailored to circles, making it the correct choice.