2/(y-3)+1=3/(y^2-9)
2/(y-3)+1=3/{(y+3)(y-3)}
分母不为零：y≠-3,y≠3
两边同乘以{(y+3)(y-3)}
2(y+3)+(y+3)(y-3)=3
y^2+2y=6
(y+1)^2=7
y=-1±根号7