通分：(1)1/a+1,3/1-a,5/a^2-1(2)a/a-b,b/a^2-b^2,c/a+b^2(3)a/a^2-

(1)
1/a+1=(A-1)/(A方-1)
3/1-a=-(3A+3)/(A方-1)
5/a^2-1
(2)
a/a-b=[A(A+B)(A+B方]/[(A方-B方)(A+B方)]
b/a^2-b^2=B(A+B方)/[(A方-B方)(A+B方)]
c/a+b^2 =C(A方-B方)/[(A方-B方)(A+B方)]
(3)
a/a^2-4=A(A-2)/[(A+2)(A-2)方]
a-1/a-2=(A-1)(A方-4)/[(A+2)(A-2)方]
a+2/a^2-4a+4 =(A+2)方/[(A+2)(A-2)方]