Question

How do you express `cos((27pi)/8)` as a trig function of an angle in Quadrant I?

Answer 1

`- cos ((3pi)/8)`

Explanation:

On the unit circle,
`cos ((27pi)/8) = cos ((11pi)/8 + 2pi) = cos ((11pi)/8) =`
`= cos ((3pi)/8 + pi) = - cos ((3pi)/8)`