Finding Radian Measure Find the number of radians in: - one-fourth of a circle. radians half of a semicircle, or a fourth of 2 a full 1 () or (2) 1 2 2 IT 4 1 4 2 two-thirds of a circle. rad. 2 2 2 4 rad. 3 3 1 3 Examining Arc Length When r = 1 2 S " If the radius of a circle is equal to 1: The unite for the oral S 2(1) 2 2T S= K S=0 0 0 =1 J = 360