What is Half of 2pi/3

I s that cos (2pi/3) or cos^2 (pi/3) ?

1/2 of 2 = 1

cos (2pi/3) = - 1/2

cos (pi/3) = 1/2

cos^2 (pi/3) = 1/4

take your pick!

pi/3 radians = 60 degrees, and cos is looking for the side adjacent to the 60 degree angle

in a 30-60-90 triangle, the sides are in the ratio 1-sqrt (3) - 2

so cos 60 = 1/2

2 (pi/3) = 120 degrees - - the same triangle, except now, x is negative = = > cos 2pi/3 = - 1/2