1.
ctg(pi\6) = cos(pi\6)/sin(pi\6) = (sqrt(3)\2)\ (1\2) = sqrt(3) - т.е. корень из 3
sin(2pi\3) = sin(pi - pi\3) = sin(pi\3) = sqrt(3)\2
2*(sqrt(3)\2 ) - sqrt(3) = 0
2. tg(pi\3) = sin(pi\3)\cos(pi\3) = (sqrt(3)\2)\ (1\2) = sqrt(3)
cos(5pi\6) = cos(pi - pi\6) = -cos(pi\6) = -sqrt(3)\2
2(-sqrt(3)\2) + sqrt(3) = 0