0.625*0.625*0.625*0.625*0.625*0.625*0.625*0.625*0.625*0.625*0.625*8*8*8*8*8*8*8*8*8*8*8*2*2*2*2*2*2*2*2*2*2*2*2=
=0.625*8*2*(0.625*8*2)*…*(0.625*8*2)
=10*10*10…*10
=100000000000
2009*19991999-1999*20092009=
2009*1999*10001-1999*2009*10001=0
0.625*0.625*0.625*0.625*0.625*0.625*0.625*0.625*0.625*0.625*0.625*8*8*8*8*8*8*8*8*8*8*8*2*2*2*2*2*2*2*2*2*2*2*2=
=0.625*16*0.625*16*…*0.625*16=10*10*10…*10 =100000000000
2009*19991999-1999*20092009=2009*1999*10001-1999*2009*10001=0