## Precalculus (6th Edition) Blitzer

$\dfrac{\sqrt3}{2}$
RECALL: (1) $\sin{\theta} = \dfrac{\text{opposite side}}{\text{hypotenuse}}$ (2) $\tan{\theta} = \dfrac{\text{opposite side}}{\text{adjacent side}}$ (3) $\cos{\theta} = \dfrac{\text{adjacent side}}{\text{hypotenuse}}$ Use formula (3) above. Use the 30-degree angle of the triangle on the right to obtain: $\cos{30^o} = \dfrac{\sqrt3}{2}$