If the arc length is equal to the diameter of the circle then what is the central angle in radians?

Correct answer: 2

Using the arc-length formula \(s=r\theta\), we get \(\theta=\frac{s}{r}\). Here the arc length equals the diameter, so \(s=2r\). Therefore, \(\theta=\frac{2r}{r}=2\) radians. \(\pi\) radians represents a semicircle, whose arc length is \(\pi r\), not \(2r\). Exam tip: To find an angle in radians, use \(\theta=\frac{s}{r}\).