cos4x=cos²2x-sin²2x=cos2x+sin2x(cos2x+sin2x)(cos2x-sin2x)-(cos2x+sin2x)=0(cos2x+sin2x)(cos2x-sin2x-1)=0cos2x+sin2x=0,cos2x-sin2x=1cos2x+sin2x=0√2sin(2x+π/4)=02x+π/4=kπx=kπ/2-π/8cos2x-s...