Radian angle, circular arc and sector
Radian measure is arc length divided by radius.
Key knowledge
A circular central angle has radian measure θ=s/r. One complete turn is 2π radians or 360 degrees. An arc has length rθ, and its sector has area r²θ/2.
Values and equations
θ=s/r; s=rθ; A_sector=(1/2)r^2θ; 360°=2π rad
- θ
- Nonnegative central angle rad
- s, r
- Arc length and positive radius length
- A_sector
- Sector area length²
Conditions and scope
- Use a Euclidean circle with radius r>0 and matching length units.
- For the ordinary non-overlapping sector, 0≤θ≤2π; use radians in the displayed formulas.
Circular Euclidean arcs/sectors; orbital and circular-speed examples excluded.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Checked the stated radian angle, circular arc and sector and restrictions against the listed primary sections; exact inspected boundaries are in the author receipt.
2026-10-10 · Independent Physics and Measurement reference editor (AI editorial bounded review). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
Entry details
Permanent link to this entry ↗- Record identity
- foundation-math-radians-arcs
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions