Question

How do you find the exact value of cos 5pi/3?

Answer 1

`1/2`

Explanation:

The angle `(5pi)/3" is located in the 4th quadrant "`

where the cos ratio has a positive value.

The 'related' acute angle is `(2pi - (5pi)/3) = pi/3`

and so `cos((5pi)/3) = cos(pi/3)`

Using the `color(blue)" Exact value triangle for this angle"`

`rArr cos((5pi)/3)=cos(pi/3)=1/2`