вычислите cos(t-2П),ctg(-t),sin(4П-t),если tgt= -√5/2, П/2

сos(t - 2π) = cos(2π - t) = cost
cos^2t = 1/(tg^2t + 1)
cos^2t = 1/(5/4 + 1)
cos^2t = 4/9
cost = -(2/3)
cost = (2/3)

ctg(-1) = - ctgt,  tgt = -√5/2, tgt*ctgt = 1,ctgt = 1/tgt,  ctgt = 1/(-√5/2)
sin(4π - t) = sint 
sint = √(1 - cos^2x) = √[1 - (2/3)^2] = √5/3

спасибо, спасла