-99+(-98)+-(-97)+...+97+98+99+100
= (-99 +99) + (-98+98)+(-97+97)+...+(-1+1) +0 +100
= 100
- 99 + ( - 98 ) + ( - 97 ) + .... + 97 + 98 + 99 + 100
= ( - 99 + 99 ) + ( - 98 + 98 ) + ( - 97 + 97 ) + ... + 100
= 0 + 0 + 0 + .... + 100
= 100
Ta có : -99+-98+-97+....+97+98+99+100
= [( -99 ) + 99 ] + [ (-98)+98] +...+0+ 100
= 0 +0+...+0+100
=100
Vậy tổng trên = 100