Question

Find all c in the interval [pi,2pi] such that 2cosx=1

Answer 1

This is a general knowledge problem, not a calculation problem.

On \([\pi,2\pi]\), the cosine is positive only on \([3\pi/2,2\pi]\), so don't look in Quadrant III.

One of the values you should just memorize it \(x = \pi/3\), which is the same as \(x = \ 2\pi - \pi/3 = 5\pi/3\). What is the cosine of that?

Answer 2

I'm sorry i'm completely lost, I have no idea what you're talking about. is there one answer to this question or multiple?

Answer 3

Are you acquainted with the Unit Circle and its important points to memorize? That is how you solve this problem.

Here's one.

http://www.snow.edu/jonathanb/Courses/Math1060/unit_circ_trig.html

Ponder it deeply. Where is the cosine equal to 1/2?