Suma conține (49+1):2 = 50:2 = 25 termeni.
[tex]\it 1=1+0\\ \\3=1+2\\ \\ 5=1+4\\ \\ 7=1+6\\ \\ .\\.\\.\\ 49=1+48\\ \rule{70}{0.6}\\ \\ n=\underbrace{\it1+1+1+\ ...\ +1}_{25\ termeni}+2+4+6+\ ...\ +48=25+2(1+2+3+\ ...\ +24)=\\ \\ \\ =25+2\cdot\dfrac{24\cdot25}{2}=25+24\cdot25=25\cdot(1+24)=25\cdot25=25^2[/tex]
