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5+10+20+...+20+....100 va rog raspusuri corecte va rog frumos


Răspuns :

=5×1+5×2+5×3+5×4+...+5×20=
=5(1+2+3+...+20)=

[tex]=5*\frac{20*21}{2}=[/tex]

[tex]=5*10*21=[/tex]

[tex]=105*10=[/tex]

[tex]\boxed{=1.050}[/tex]


OBS!!!
SUMA LUI GAUSS:

[tex]\boxed{1+2+3+...+n=\frac{n(n+1)}{2}; n \in |N}[/tex]