1998*1999/1998+1999*2000/1998+…+2049*2050/1998
=（1998/1-1999/1+1999/1-2000/1+……+2049/1-2050/1）/1998
=（1998/1-2050/1）/1998
=1-2050/1998
=2050/52
=1025/26