Mathematics

Segment of a Circle

Last updated: 13 February 2026

What Is a Segment of a Circle?

A segment of a circle is the geometric region bounded by a chord and the arc it subtends. A chord is defined as a line segment joining any two points on the circle's circumference (Barbara E. Reynolds et al., 2012)(Steve Slavin et al., 2004). While an arc represents a curved portion of the circle, the chord serves as the straight boundary of the segment (Steve Slavin et al., 2004). This distinguishes a segment from a sector, which is bounded by an arc and two radii (Barbara E. Reynolds et al., 2012).

Structure and Composition of a Segment

The composition of a segment depends on the length of its chord and the curvature of its arc. A diameter is a special type of chord that passes through the center of the circle (Amol Sasane et al., 2015). This specific chord is the longest possible in a circle and divides the entire area into two equal segments called semicircles (Steve Slavin et al., 2004). Any other chord creates a major and minor segment based on the arc's size (Steve Slavin et al., 2004).

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Geometric Properties and Relationships

Geometric properties of segments are often derived from the relationship between the center and the chord. For example, the line joining the center of a circle to the midpoint of a chord is always perpendicular to that chord (Amol Sasane et al., 2015). Furthermore, the measure of an arc can be defined by the central angle it subtends, which directly influences the area and proportions of the resulting segment (Barbara E. Reynolds et al., 2012).

Comparative Analysis of Related Structures

A segment of a circle is often compared to other circular regions like sectors and semicircles. While a sector is bounded by an arc and two radii (Barbara E. Reynolds et al., 2012), a segment is defined by an arc and a single chord (Steve Slavin et al., 2004). Understanding these distinctions is vital for applying segment relationship formulas, such as those used when calculating lengths in intersecting chords or angles formed by tangents and secants (Daniel C. Alexander et al., 2014).

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