Question

( 1 +2 +...+ 20) divizibil cu (1 + 2 +...+ 5)

Answer 1

1+2+...+20=20*21/2=210
1+2+...+5=5*6/2=15

210=15*14
Deci ( 1 +2 +...+ 20) divizibil cu (1 + 2 +...+ 5)

Answer 2

 [tex](1+2+...+20)\\ Aplicam~suma~Gauss~cu~formula:[n(n+1)]/2\\ =\ \textgreater \ \frac{20*21}{2} =\ \textgreater \ 10*21=\ \textgreater \ 210\\\\ (1+2+...+5)\\ Aplicam~suma~Gauss~cu~formula:[n(n+1)]/2\\ =\ \textgreater \ \frac{5*6}{2} =\ \textgreater \ 5*3=15\\\\ 210|15=\ \textgreater \ 210:15=14=\ \textgreater \ propozitia~este~adevarata[/tex]