(1)令(x^2-5x)/(x+1)=t,則(x+1)/(x^2-5x)=1/t,所以原方程換元后為t+24/t+14=0,方程兩邊同時乘以t得t^2+14t+24=0解得t=-2或t=-12即(x^2-5x)/(x+1)=-2或(x^2-5x)/(x+1)=-12,
解(x^2-5x)/(x+1)=-2得: x=1或x=2
解(x^2-5x)/(x+1)=-12得: x=-3或x=-4
（2）令(x^2+1)/(x+1)=t,(x+1)/(x^2+1)=1/t,所以原方程換元后為2t+6/t=7,方程兩邊同時乘以t得2t^2+6=7t,解得t=2或t=3/2即(x^2+1)/(x+1)=2或(x^2+1)/(x+1)=3/2
解(x^2+1)/(x+1)=2得: x=1+√2或x=1-√2
解(x^2+1)/(x+1)=3/2得: x=(3+√17)/4或x=(3-√17)/4
(3)(x^4+2x^2+1)/x^2+(x^2+1)/x=(x^2+1)^2/x^2+(x^2+1)/x=[(x^2+1)/x]^2++(x^2+1)/x
令(x^2+1)/x=t,則原方程換元后為t^2+t=2,解得t=-2或t=1即(x^2+1)/x=1或(x^2+1)/x=-2
解(x^2+1)/x=1得：無解
解(x^2+1)/x=-2得：x=-1