利用二倍角公式和辅助角公式f (x)=-根号2sin²x+根号2sinxcosx=-(√2/2)(1-cos2x)+(√2/2)sin2x=(√2/2)sin2x+(√2/2)cos2x-√2/2=sin2x*cos(π/4)+cos2x*sin(π/4)-√2/2=sin(2x+π/4)-√2/2...