[3x/(x-1) - x/(x+1)]÷ x/(x²-1)=[3x/(x-1) - x/(x+1)] * (x²-1)/x=[3x/(x-1)]* (x²-1)/x - [x/(x+1)] * (x²-1)/x=3(x+1) -(x-1)=3x+3-x+1=2x+4=2(根号2-2）+4=2根号2 - 4+4=2根号2