(x^2+1)/(x+1)+3(x+1)/(x^2+1)=4 令t=(x^2+1)/(x+1)t+3/t=4t+3/t-4=0t^2-4t+3=0(t-3)(t-1)=0t=1或t=3当t=1时(x^2+1)/(x+1)=1x^2+1=x+1x^2-x=0x(x-1)=0x=0或x=1当t=3时(x^2+1)/(x+1)=3x^2+1=3x+3x^2-3x-2=0x^2-3x+9/4...