Another representation in polar coordinates of the point (1 5 pi/6) is

Hello : 
note : the polar coordinates is : (r , θ)
Another representation is  (x, y)   : x=r cos(θ)   and y = sin(θ) and : r =√(x²+y²)
in this exercice : r = 1    and  θ = 5π/6 
so : x= 1.cos(5π/6)   and y = 1. sin(5π/6)
but : cos(5π/6)  = cos (π - π/6) = - cos(π/6 ) = (- √3)/2
        sin(5π/6)  = sin (π - π/6) =  sin(π/6 ) =1/2
Another representation  is : ( (- √3)/2 , 1/2)

Subtracting is the opposite of adding