From Förberedande kurs i matematik 1

If we express the angle \displaystyle \text{33}0^{\circ } in radians, we obtain

\displaystyle \text{33}0^{\circ }=\text{33}0^{\circ }\centerdot \frac{\pi }{180^{\circ }} radians \displaystyle =\frac{11\pi }{6} radians

and from exercise 3.3:1g, we know that

\displaystyle \cos 330^{\circ }=\cos \frac{11\pi }{6}=\frac{\sqrt{3}}{2}.