1/2*(sin2x-cos2x)-1/2 括号内提取√2
=√2/2*(√2/2xin2x-√2/2cos2x)-1/2
=√2/2*(sin2xcosπ/4-cos2xsinπ/4)-1/2
=√2/2*sin(2x-π/4)-1/2
你的题中是=√2/2*sin(2x+π/4)-1/2错了.