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Calculeaza sumele: a) 2+4+6+...+2018 b) 5+10+15+...+2020

Răspuns :

a) 2(1+2+3+...+1009)=2x 1009(1+1009):2 = 1009 x 1010 = 1019090
b) 5(1+2+3+...+405) = 5x405x406:2= 2020 x 203 = 410060
Sume Gauss.