(1997^3-2*1997^2-1995)/(1997^3+1997^2-1998)
=[1997^2*(1997-2)-1995]/[1997^2*(1997+1)-1998]
=[(1997^2-1)*1995]/[(1997^2-1)*1998]
=1995/1998
(1997^3-2*1997^2-1995)/(1997^3+1997^2-1998)
=[1997^2*(1997-2)-1995]/[1997^2*(1997+1)-1998]
=[(1997^2-1)*1995]/[(1997^2-1)*1998]
=1995/1998