3/(x+1)+1/(x-1)=6/(x^2-1)
{3(x-1)+(x+1)}/(x^2-1)=6/(x^2-1)
(3x-3+x+1)/(x^2-1)=6/(x^2-1)
4x-2=6①
x^2-1≠0②
由①得：x=2