13a) cos α = 1/2 sin α = +-√(1-(1/2)²) =+- √(1-(1/4)) = +-√3/2.
б) cos α = -2/3 sin α = +-√(1-(-2/3)²) =+- √(1-(4/9)) = +-√5/3.
в) cos α = -1 sin α = 0.
14а) sin α = √3/2 cos α = +-√(1-(√3/2)²) = +-√(1-(3/4)) = +-1/2.
б) sin α = 1/4 cos α = +-√(1-(1/4)²) = +-√(1-(1/16)) = +-√15/4.
в) sin α = 0 cos α = 1.
15 а) cos α = 1 tg α = 0.
b) cos α = -√3/2 tg α = +-√(1-(-√3/2)²) / (-√3/2) = +-1/√3.
c) cos α = √2/2 0 < α = 90 tg α = 1.
d) cos α = 3/5 90 < α = 180 tg α = -√(1-(3/5)²) / (3/5) = -4/3.