\(M=\left\{-20;-19;-18;...;18;19;20\right\}\)
Tổng các phần tử:
\(-20+-19+-18+...+18+19+20\)
\(=\left(-20+20\right)+\left(-19+19\right)+\left(-18+18\right)+...+\left(-1+1\right)\)
\(=0+0+0+...+0\)
\(=0\)
M={−20;−19;−18;...;18;19;20}
Tổng các phần tử:
−20+−19+−18+...+18+19+20
=(−20+20)+(−19+19)+(−18+18)+...+(−1+1)
=0+0+0+...+0
=0