Radians, arc length and sector area

By the end you’ll be able to

• Convert angles between degrees and radians.
• Interpret one radian as the angle subtended by an arc equal in length to the radius.
• Use the formula $s=r\theta$ for arc length with $\theta$ in radians.
• Use the formula $A=\tfrac12 r^2\theta$ for sector area with $\theta$ in radians.