How do you evaluate cos((2pi)/3)?

1 Answer
Jim G.
Apr 25, 2016

-1/2

Explanation:

The angle (2pi)/3" is in the 2nd quadrant "
where the cos ratio has a negative value.

The related 'acute angle' to (2pi)/3 =( pi -(2pi)/3) = pi/3

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

and using the color(blue)" Exact value triangle"

enter image source here

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

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