1999×(1-2/1)×(1-3/1)×(1-4/1)×……×(1-1999/1) =1999×(1/2)×(2/3)×(3/4)*(4/5)×.......(1998)/1999 =1999×(1/1999) =1.
1999×(1-2/1)×(1-3/1)×(1-4/1)×……×(1-1999/1)
=1999×(1/2)×(2/3)×(3/4)*(4/5)×.......(1998)/1999
=1999×(1/1999)
=1.
1999×(1-2/1)×(1-3/1)×(1-4/1)×...×(1-1999/1)
=1999×2/1×3/2×...×1999/1998
=1999×1999/1
=1
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