3*5/1+5*7/1+7*9/1+...+199

3*5/1+5*7/1+7*9/1+...+1997*1999/1=

1个回答

1/3*5+1/5*7+1/7*9+……+1/1997*1999
=（1/3-1/5+1/5-1/7+1/7-1/9+……+1/1997-1/1999）*(1/2)
=（1/3-1/1999）*(1/2)
=998/5997