## Trigonometry 7th Edition

$2 \sqrt 3$
Given expression = 4 $\cos( z - 30^{\circ})$ = 4 $\cos(60^{\circ} - 30^{\circ})$ ( replacing z with $60^{\circ}$) = 4 $\cos 30^{\circ}$ = 4 $\times (\frac{\sqrt 3}{2})$ ( substituting for exact value of $\cos 30^{\circ}$) = $2 \sqrt 3$