Ф =5π/6
The reference angle is the smallest angle that the terminal side of the angle makes with the x-axis.
Given that here π/2 < Ф < π, the angle is in the second quadrant.
In the second quadrant the signs are:
sine positive
cosine negative
tangent negative.
Furthermore, the reference angle is π - Ф = π - 5π/6 = π/6.
Then,
sin Ф = sin π/6 = 1/2
cos Ф = - cos π/6 = -√(3) / 2
tan Ф = - tan π/6 = -√(3) /3
