（1）1/x +2/x-3 =0
1/x =-2/x-3
1/x =2/3-x
2x =3-x
3x =3
x =1
（2）1/ x2+x - 1/x2 -1 =0
1/ x2+x=1/x2 -1
x2+x=x2 -1
x =-1