cos2x-sin2x
=√2（cos2x*√2/2-sin2x*√2/2)
=√2（cos2x*cosπ/4-sin2xsinπ/4)
=√2cos(2x+π/4)
cos2x-sin2x
=√2（cos2x*√2/2-sin2x*√2/2)
=√2（cos2x*sinπ/4-sin2xcosπ/4)
=√2sin(2x-π/4)
两个一样的最大值都是根号2　最小值都是－根号2吧　！！嗯