Tìm x: (-100 + 99 - 98 +...-2 + 1) - x = 15

1/ (-100+99-98+...-2+1)-x=15

2/ (-50-49-48-...+1+0+1+2+...+49)+x= -45

3/ x+(x-1)+(x-2)+...+(x-100)=99+99.2+99.3+...+99.101