6)(1+cos2x)/2=1/21+cos2x=1cos2x=02x=π/2+πn,n∈Zx=π/4+πn/2,n∈Z7)cos(x/9)=1/2x/9=+-π/3+2πn,n∈Zx=+-3π+18πn,n∈Z8)3x-π/4=π/3+πn,n∈Z3x=7π/12+πn,n∈Zx=7π/36+πn/3,n∈Z9)sin(x/3)=√40/5>1 нет решения10)сosx(8cosx-3)=0сosx=0⇒x=π/2+πn,n∈Zcosx=3/8⇒x=+-arccos3/8+πk,k∈Z