a, x-10/1994+x-8/1996+x-6/1998+x-4/2000+x-2/2002=x-2002/2+x-2000/4+x-1998/6+x-1996/8+x-1994/10
=>,x-10/1994-1+x-8/1996-1+x-6/1998-1+x-4/2000-1+x-2/2002-1+4=x-2002/2-1+x-2000/4-1+x-1998/6-1+x-1996/8-1+x-1994/10-1+4
=> x-2004/1994+x-2004/1996+x-2004/1998+x-2004/2000+x-2004/2002=x-2004/2+x-2004/4+x-2004/6+x-2004/8+x-2004/10
​=>x-2004/1994+x-2004/1996+x-2004/1998+x-2004/2000+x-2004/2002- x-2004/2-x-2004/4-x-2004/6-x-2004/8-x-2004/10=0
=>x-2004(1/1994+1/1996+1/1998+1/2000+1/2002-1/2-1/2-1/6-1/8-1/10)=0
=>x-2004=0
=>x=2004
b,
x-1991/9+x-1993/7+x-1995/5+x-1997/3+x-1999/1=x-9/1991+x-7/1993+x-5/1995+x-3/1997+x-1/1999
=>x-1991/9-1+x-1993/7-1+x-1995/5-1+x-1997/3-1+x-1999/1-1+4=x-9/1991-1+x-7/1993-1+x-5/1995-1+x-3/1997-1+x-1/1999-1+4
=>x-2000/9+x-2000/7+x-2000/5+x-2000/3+x-2000/1=x-2000/1991+x-2000/1993+x-2000/1995+x-2000/1997+x-2000/1999(triệt tiêu 4)
=>x-2000/9+x-2000/7+x-2000/5+x-2000/3+x-2000/1-x-2000/1991-x-2000/1993-x-2000/1995-x-2000/1997-x-2000/1999=0
=>x-2000(1/9+1/7+1/5+1/3+1/1-1/1991-1/1993-1/1995-1/1997-1/1999)=0
=>x-2000=0
=>x=2000
chúc bạn học tốt