По таблице значений
sin (-2/3π)= -√3/2
tg7/6=√3/3
cosπ/2-ctg5/4π=0-1=-1
ctgπ/3tg(-π/3)-cos(-π)sinπ=√3/3*√3-(-1)*0=1
tg720+sin540-ctg135=tg0+sin180-ctg135=0+0-(-1)=1
tg²t(-1+1/sin²t)=tg²t*ctg²t=1
sint=√3/2 t=π/3+2πk t=2π/3+2πk, k∈Z
sin(π/2+t)=-1/2 cost=-1/2 t=+/-2π/3+2πk, k∈z