Circular Measure uses radians to measure angles: $\pi$ radians $=180°$.
Formulae (θ in radians)
Arc length $= r\theta$ · Sector area $= \tfrac12 r^2\theta$
Example: arc length with $r=5$, $\theta=2$ is $5\times 2 = 10$.
Remember
- $\pi$ rad $=180°$; $2\pi$ rad $=360°$.
- Arc $=r\theta$ · Sector $=\tfrac12 r^2\theta$.