Question

Evaluate a) sin (4pi/3) b) cos (5pi/6)

Answer 1

Sin(pi + a) = -sin(a)
sin(4pi/3) = sin(pi + pi/3) = -sin(pi/3)

cos(pi-a) = -cos(a)
cos(5pi/6) = cos(pi -pi/6) = -cos(pi/6)

Answer 2

A) sin ( 4π/3 ) = sin 240° = sin ( 180° + 60°) = - sin 60° = $- \frac{ \sqrt{3} }{2}$

b) cos (5π/6 ) = cos 150° = cos ( 90° + 60° ) = - sin 60°=$- \frac{ \sqrt{3} }{2}$