Question

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

Answer 1

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

$=5*\frac{20*21}{2}=$

$=5*10*21=$

$=105*10=$

$\boxed{=1.050}$


OBS!!!
SUMA LUI GAUSS:

$\boxed{1+2+3+...+n=\frac{n(n+1)}{2}; n \in |N}$