1) cos(π/3) = 1/2
sin(3π/4) = √2/2
tg(π/6) = 1/√3
ctg(π/3) = 1/√3
2) arccos(1/2) = π/3
arcsin(√2/2 = π/4
arctg(√3 = π/3
arcctg(1) = π/4
3) sint = 4/5
π/2 < t < π вторая четверть, значит будет знак "-"<br>cost = - √(1 - sin^2t) = -√(1 - 16/25) = - √(9/25 = - 3/5
tgt = sint/cost
tgt = (4/5)/(-3/5) = - 4/3
ctgt = 1/tgt = - 3/4