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Calculeaza suma: 11+22+33+...+198


Răspuns :

11+22+33+...+198=11*(1+2+3+....+18)=in   paranteza    ai    o    suma   gauss=11*(18*19)/2=1881
11+22+33+...+198=
=11(1+2+3+...+18)=
=11×18×19:2=
=3762:2=
=1881

sau

S=11+22+33+...+198
S=198+197+...+11

2S=209+209+...+209
2S=209×18
2S=3762
S=3762:2
S=1881