Definitions
A circle is a two-dimensional pattern that consists of all the points that are within a certain distance from a given central point. The circle is named after its central point.
Circle - related definitions
- The perimeter of a circle is a plane curve that consists of all the points that have the same distance from the circle's centre.
- The radius of a circle is a segment that connects the centre of the circle with a point at its perimeter.
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A chord is a segment that connects two points on the circumference of a circle.
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The diameter is the chord that passes through the circle's central point.
- A tangent is a line that flanks a circle at one point.
- Two points on the perimeter of a circle divide its circumference into two arcs.
Parts of a circle O
- radius OC
- diameter AB or chord DE
- chord DE
- arc CB
Areas of a circle
- A sector is an area of a circle bounded by two radii.
- A sector's central angle [[$\alpha$]] has its vertex at the circle's centre.
- A chord divides the circle into two segments.
Since each chord divides a circle into two segments, it is important to clearly mark which segment is meant. The same applies to sectors.
The diameter of a circle
The diameter [[$ d $]] of a circle is twice the length of its radius [[$ r $]].
[[$d = 2r$]]