1.(1/1998-1)×(1/1997-1)×(1/1996-1)...(1/1001-1)×(1/1000-1) =-1*(1997/1998)*(1996/1997)*(^^^^^省略^^^^^)*(999/1000)=-999/1998=-1/22.1/3×7+1/7×11+1/11×15+...+1/55×59=(1/4)*(1/3-1/7+1/7-1/11^^^省...