y=(x+1)/(x^2+2x+2)分母配方y=(x+1)/[(x+1)^2+1]x=-1,x+1=0,y=0x+1不等于0时分子分母同除（x+1)y=1/[(x+1)+1/(x+1)]分母使用均值定理(x+1分正负讨论)(x+1)+1/(x+1)小于等于-2或大于等于2x+1不等于0时,y值域{y|-1/2...