What do R, R, D, S, C, π in the circle mean? And the area formula and perimeter formula of the circle? thank you

Radius of the circle: r (R also represents the radius of the circle)

Diameter: d

Pi: π (the value is 3. 14 15926535 ... infinite cycle decimal), and 3. 14 is usually used as the value of π.

The formula of the circumference of a circle c = 2π r

The area formula of a circle s = π r?

The area of a semicircle is half the area of a circle, and the circumference of a semicircle is half the circumference of a circle plus the length of two radii.

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