Question

What is the exact value for cos(-2$\pi$/3)?
This should be done without a calculator.
Please explain the process if possible.

Answer 1

notice the picture below

see where that angle is?

check your Unit Circle for that value

also notice, that fractions of $\pi$ are just like grabbing 180 degrees and splitting it, so one third of 180 or $\pi$ is 180/3 or 60 degrees