# Practice problems of the circle

A circle is a geometric shape that consists of all points that are a fixed distance, called the radius, away from a central point called the center. The distance around the circle is called the circumference and the region enclosed by the circle is called the area of the circle. The formula for the circumference of a circle is C = 2πr, where C is the circumference, r is the radius, and π is a mathematical constant, the Ludolph number, approximately equal to 3.1415926.

The formula for the area of a circle is A = πr2, where A is the area and r is the radius.

The diameter of a circle is a line segment that passes through the center of the circle and has its endpoints on the circle. It is the longest distance across the circle and is also twice the length of the radius. The formula for the diameter of a circle is d = 2 * r, where d is the diameter and r is the radius. The diameter of a circle is an important measurement in geometry and is used in many mathematical formulas, such as the formula for the circumference of a circle (C = πd)

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