### Answer:

An angle of 2Ο rads us 1 revolution so 6Ο is 3 revolutions. cos(0) = 1, cos(2Ο) = 1, cos(6Ο) = 1.Β

An angle of Ο/2 is a quarter turn or right angle anticlockwise so an angle of β Ο/2 is a quarter turn or right angle clockwise. Therefore, 11Ο/2 is 11 right angles clockwise which is 2 3/4 full turns. Sin(Ο/2) = 1, sin(-Ο/2) = -1, cos(-11 Ο/2) = sin(Ο/2) = 1

It’s easy!