Chapter 3 - Radian Measure and the Unit Circle - Section 3.3 The Unit Circle and Circular Functions - 3.3 Exercises - Page 123: 4

$\frac{\sqrt 3}{2}$

An angle of $\frac{\pi}{3}$ radians intersects the unit circle at the point $(\frac{1}{2},\frac{\sqrt 3}{2}$) as we saw in the solution of excercise 1. Because, $\sin s=y$ $\sin \frac{\pi}{3}=\frac{\sqrt 3}{2}$.