Question

cos 2p/3 =

sin(-11p/4)=

tg 17p/6=

ctg (-p/4)

Answer 1

1)-1/2
2)-√2 /2
3)-√3 /3
4)-1 
№3:

Tg 17p/6=tg(2p+p-p/6 )=tg(p/6)=-√3 /3

№2:

sin(-11p/4)=sin(2p-3p/4)=sin(3p/4)=-√2 /2