设sinx+cosx=t属于[-根号2,根号2] => t^2=1+2sinxcosx =〉 sinxcosx=(t^2-1)/2f(x）=（t^2-1）/2(1+t)=(t-1)/2属于[-(√2+1)/2,(√2-1)/2]另外,分母不为零,所以1+sinx+cosxb不=0 ,既t不=-1 综上,值域属于[-(√2+1)/2...