sin(2x－π/4)－2√2sin^2x
=sin2xcos(π/4)-cos2xsin(π/4)-√2(1-cos2x)
=√2/2(sin2x+cos2x)-√2
=sin(2x+π/4)-√2=√2/2(sin2x+cos2x)-√2=sin(2x+π/4)-√2就是这两步不懂，sinπ/4=cosπ/4=√2/2,sin(A+B)=sinAcosB+cosAsinB√2/2(sin2x+cos2x)-√2=sin2xcosπ/4+cos2xsinπ/4-√2=sin(2x+π/4)-√2看明白吗？你要记住一些基本公式哦。祝你进步！晕，，，，居然没想到同时提取2√2………谢了哈～