sin^2 x/6=1/2
2cos^2x+cos10x-1=0

1)(1-cosx/3)/2=1/21-cosx/3=1cosx/3=0x/3=π/2+πnx=3π/2+3πn2)cos2x+cos10x=02cos6xcos4x=0cos6x=0⇒6x=π/2+πn⇒x=π/12+πn/6cos4x=0⇒4x=π/2+πn⇒x=π/8+πn/4