Notes
circle

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Circle

A circle is a shape defined by the property that every point on the circle is a fixed distance from a specified centre point.

A line segment from the centre to a point on the circle is called a radius, and its length is called the radius of the circle.

A diameter of the circle is a line segment that joins two points on the circle which also passes through its centre. Its length is called the diameter of the circle.

Circumference

The perimeter of a circle is also called its circumference. A circle with radius rr has circumference 2πr2 \pi r.

Area

The area of a circle of radius rr is πr 2\pi r^2.

Symmetry

A circle has many symmetries: every rotation about its centre and every reflection in a line through its centre.

Many results involving circles begin with the fact that any triangle with one vertex at the centre and the other vertices on the circle must be isosceles as two of its sides are radii of the circle and hence the same length.

category: shape
category: definition
category: circle theorems

Revised on May 6, 2022 15:59:17 by Andrew Stacey
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