Mariamoldoveanu6297ask
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DAU COROANA JUR!
5+10+15+20+...+2020
Va rog​

Răspuns :

Mikelinaask

5+10+15+20+...+2020, dam factor comun pe 5

5(1+2+3+...+404)

1+2+3+...404= aplicam formula lui Gauss

5[404×(404+1):2]=

5(404×405:2)=

5(202×405)=

5×81810=

409050

Alesia03ask

5+10+15+20+............+2020=

=5×1+5×2+5×3+............+5×404=

=5×(1+2+3+.........+404)=

=5×(404×(404+1)÷2)=

=5×(163620÷2)

=5×81810

=409050