a)-20<x<-21
Vi -20va-21 la 2so nguyen am lien tiep
nen=>ko co so x nao ma >-20va<-21
b)-18≤x≤17
=>x∈{-18,-17,...,16,17}
Tong cac so nguyen x la: (-18)+(-17)+...+16+17=-18
c)-27<x≤27
=>x∈{-26,-25,....,26,27}
Tong cac so nguyen x la: (-26)+(-25)+....+26+27=27
d)|x|≤3
=>|x|∈{0,1,2,3}
=>x∈{-3,-2,-1,0,1,2,3}
Tong cac so nguyen x la: (-3)+(-2)+(-1)+0+1+2+3=0
e)|-x|<5
=>|-x|∈{0,1,2,3,4}
=>-x∈{-1,-2,-3,-4}
Tong cac so x la: (-1)+(-2)+(-3)+(-4)=-10