# Chapter 6 - The Circular Functions and Their Graphs - 6.2 The Unit Circle and Circular Functions - 6.2 Exercises - Page 589: 70

$s=\dfrac{2\pi}{3}$

#### Work Step by Step

Use the inverse cosine function of a calculator in radian mode to obtain: $s=\cos^{-1}{(-\frac{1}{2})} = \frac{2\pi}{3}$

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