Precalculus (6th Edition) Blitzer

From the property of the cosine function, $\cos \left( -\theta \right)=\cos \theta$ The value of $\cos \frac{\pi }{6}$ is $\cos \frac{\pi }{6}=\frac{\sqrt{3}}{2}$ Thus, the value of $\cos \left( -\frac{\pi }{6} \right)$ is $\frac{\sqrt{3}}{2}$. So, the statement is false.