= 3977958+34034+2020/2003x(2004-2)
= 4014012/2003x2004
= 2004/2002
= 1002/1001
2003*1986+2002*17+2020 / 2003*2004-2003*2003
= 2003*1986+[ 2003-1]*17+2020/ 2003*2004-2003*2003
= 2003*1986+2003*17-1*17+2020/ 2003*2004-2003*2003
=2003*[1986+17]+2020/2003*2004-2003*2003
=2003*2003-17+2020/2003*2004-2003*2003
=-2020-17/2003*2004[ cả 2 vế bỏ đi 2002*2003]
=2003/2003*2004
=1/2004