3x/x-1 +1= 4/x-1两边同时乘以x-1
3x+x-1=4
4x=5
x=1.25
1/x+1 + 2/x-1=4/x²-1 两边同时乘以x²-1
x-1+2（x+1）=4
x-1+2x+2=4
3x=3
x=1