How to calculate the diameter

The circumference of a circle divided by pi is the diameter. C=πd, which is the basic formula, where C is the circumference, π is the pi and D is the diameter. A circle is a geometric figure, which refers to the set of all points on a plane with a constant distance from a fixed point. This given point is called the center of the circle. The distance as a fixed value is called the radius of a circle.

How to calculate the radius of a circle: r.

Diameter: d

Pi: π (the numerical value is between 3. 14 15926 and 3. 14 15927 ... infinite cyclic decimal), and 3. 14 is usually used as the numerical value of π.

Area of circle: S=πr? ; S=π(d/2)？

Area of semicircle: s semicircle =(πr? ; )/2

Ring area: s great circle -S small circle =π(R? -r？ (R is the radius of the big circle and R is the radius of the small circle)

Circumference: C=2πr or c = π d.

Circumference of a semicircle: d+(πd)/2 or d+π r.