1+2+3+...+31+32+33=17×33,
1-3+2-6+3-9+4-12+...+31-93+32-96+33-99
=(1+2+3+...+31+32+33)-3x(1+2+3+...+31+32+33)
=17×33-3x17×33=-2x17×33
=-1122
1+2+3+...+31+32+33=17×33,
1-3+2-6+3-9+4-12+...+31-93+32-96+33-99
=(1+2+3+...+31+32+33)-3x(1+2+3+...+31+32+33)
=17×33-3x17×33=-2x17×33
=-1122