1/2cos2x-1/2sin2x怎么就变成二分之根号二cos(2x+π/4)

1/2cos2x-1/2sin2x怎么就变成二分之根号二cos(2x+π/4)
1/2cos2x-1/2sin2x怎么就变成二分之根号二cos(2x+π/4)

1/2cos2x-1/2sin2x怎么就变成二分之根号二cos(2x+π/4)
1/2cos2x-1/2sin2x=√2/2(√2/2COS2X-√2/2SIN2X)
=√2/2(C0Sπ/4COC2X-SINπ/4SIN2X)=√2/2cos(2x+π/4)