[tex]\displaystyle\bf\\5+6+7+...+56=?\\\\\textbf{Calculam numarul de termeni (n).}\\\\n=56-5+1=51+1=52~de~termeni.\\\\Folosim~formula~lui~Gauss:\\\\5+6+7+...+56=\frac{n(56+5)}{2}=\frac{52\times61}{2}=26\times61=\boxed{\bf1586}[/tex]
