[tex]Dam~factor~comun~pe~5:\\
9*5(1+2+3+...+40):41\\
Avem~o~suma~Gauss~aplicam~formula[n(n+1)]:2\\
=\ \textgreater \ 45(20*41):41=\ \textgreater \ 900\\
a)900~se~termina~in~0=\ \textgreater \ patrat~perfect\\
b) \sqrt{900} =30=\ \textgreater \ patrat~perfect.[/tex]
