Question

How can I tell if cos 2π/3 is a 30,60,90 triangle or a 45,45,90 triangle?

Answer 1

thats a bit weird on wording, but convert the angle from radians to degrees, and you should have your answer

Answer 2

actually, i don't think that will give you what you need.. the angle doesn't match any of your triangles, and the value of cos (2pi/3) is negative, did you write the question correctly?