1/x∈{±19,±18,±17,±16,±15,±14,±13,±12,±11,...,±2,±1,20,0}
Tổng=-19+19+-18+18+...+-2+2+-1+1+0+20=20
2/x∈{-18,±17,±16,±15,...,±2,±1,0}
Tổng =-18+-17+17+-16+16+...+-2+2+-1+1+0=-18
3/x∈{±26,±25,±24,...,±2,±1,0,27}
Tổng=-26+26+-25+25+...+-2+2+-1+1+0+27=27
4/x∈{0,±1,±2,±3}
Tổng=-1+1+-2+2+-3+3+0=0
5/x∈{±1,±2,±3,±4,0}
Tổng =-1+1+-2+2+-3+3+-4+4+0=0
