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Calculati suma: S=21+22+23+...+37

Răspuns :

S=21+22+23+...+37 =(1+2+3+....+20) +21+22+23+...+37-(1+2+3+....+20)=
=
1+2+3+....+20 +21+22+23+...+37-(1+2+3+....+20)=
=37*38/2-20*21/2=37*19-10*21=703-210=493