(1/2010-1)*(1/2009-1)*(1/2008-1)*...*(1/1001-1)*(1/1000-1)
=(-1)的1011次方*(1-1/2010)*(1-1/2009)*(1-1/2008)*...*(1-1/1001)*(1-1/1000)
=-(2009/2010)*(2008/2009)*(2007/2008)*...*(1000/1001)*(999/1000)
=-999/2010
(1/2010-1)*(1/2009-1)*(1/2008-1)*...*(1/1001-1)*(1/1000-1)
=(-1)的1011次方*(1-1/2010)*(1-1/2009)*(1-1/2008)*...*(1-1/1001)*(1-1/1000)
=-(2009/2010)*(2008/2009)*(2007/2008)*...*(1000/1001)*(999/1000)
=-999/2010