x²+x²/(x+1)²=3设t＝x+1 x=t-1(t-1)²+(t-1)²/t²=3t²-2t+1+1-2/t+1/t²=3t²+2+1/t²-2t-2/t²=3(t+1/t)²-2(t-1/t)=3 令y＝t+1/ty²-2y-3=0(y-3)(y+1)=...