Question

suppose I am given sin y = -1/2 and cos y = sqrt(3)/2, I get two different solutions.
if i do siny / cos y = tan y = (-1/2)/ (sqrt(3)/2)
tan y = -sqrt 3 / 3 , i get 5pi/6 + pi*n.
But if i do cos y = sqrt 3 / 2 , i get a different answer