4
cos(x/2-π/7)=√3/2
x/2-π/7=-π/6+2πn U x/2-π/7=π/6+2πn
x/2=-13π/42+2πn U x/2=π/42+2πn
x=-13π/21+4πn U x=π/21+4πn,n∈z
5
cos²x/4=1/2
(1+cosx/2)/2=1/2
1+cosx/2=1
cosx/2=0
x/2=π/2+πn
x=π+2πn,n∈z
7
ctg3x=-1
3x=3π/4+πn
x=π/4+πn/3,n∈z
8
sin(π/2+x)+3cosx=0
cosx+3cosx=0
4cosx=0
cosx=0
x=π/2+πn,n∈z
9
2cosx=tgπ/3
2cosx=√3
cosx=√3/2
x=+-π/6+2πn,n∈z
10
cos²x-sin²x=cosπ
cos2x=-1
2x=π+2πn
x=π/2+πn,n∈z