2△1=1/2*1+1/(2+1)(1+A)=2/3,
1/2+1/3(1+A)=2/3,
1/3(1+A)=1/6,
2=1+A,
A=1,
∴XΔY=1/XY+1/(X+1)(Y+1)
2004Δ2005
=1/2004×2005+1/2005×2006
=1/2004-1/2005+1/2005-1/2006
=1/2010012.
2△1=1/2*1+1/(2+1)(1+A)=2/3,
1/2+1/3(1+A)=2/3,
1/3(1+A)=1/6,
2=1+A,
A=1,
∴XΔY=1/XY+1/(X+1)(Y+1)
2004Δ2005
=1/2004×2005+1/2005×2006
=1/2004-1/2005+1/2005-1/2006
=1/2010012.