Đáp án+Giải thích các bước giải:
Suy ra x+11999+1+x+21998+1=x+31997+1+x+41996x+11999+1+x+21998+1=x+31997+1+x+41996
Suy ra x+20001999+x+20001998=x+20001997+x+20001996x+20001999+x+20001998=x+20001997+x+20001996
Suy ra x+20001999+x+20001998−x+20001997−x+20001996=0x+20001999+x+20001998−x+20001997−x+20001996=0
Suy ra x+2000.(11999+11998−11997−11996)=0x+2000.(11999+11998−11997−11996)=0
Vì (11999+11998−11997−11996)≠0(11999+11998−11997−11996)≠0
Suy ra x+2000=0
Suy ra x=-2000
