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计算:(2+1/2003+1/2004)x(1/2003+1/2004+1/2005)—(2+1/2003+1/2004

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计算:(2+1/2003+1/2004)x(1/2003+1/2004+1/2005)—(2+1/2003+1/2004+1/2005)x(1/2003+1/2004)
设1/2003+1/2004=x
1/2003+1/2004+1/2005=y
(2+1/2003+1/2004)x(1/2003+1/2004+1/2005)—(2+1/2003+1/2004+1/2005)x(1/2003+1/2004)
=(2+x)y-(2+y)x
=2y+xy-2x-xy
=2y-2x
=2(y-x)
=2*1/2005
=2/2005