令sinx+cosx=t则t=√2sin(x+π/4)∈[-√2,√2]t²=sin²x+cos²x+2sinxcosx=1+2sinxcosxsinxcosx=(t²-1)/2则 y=t+(t²-1)/2=(t²+2t-1)/2=[(t+1)²-2]/2当t=-1时,y有最小值-1当t=√2时...