[X（X+3）/(X+3)-(3X+1)/(X+3)]÷（X-1）²/x(x+3)=（X²-1)/（X+3）÷（x-1）²/x(X+3)=X(X+1)/(X-1）.解2X/(X+4)=1,得X=4，将X=4套入上式得，20/3/ 是分号，希望能看得懂
