Question

Aratati ca numarul 2005+2×(1+2+3+...+2004) este patrat perfect

Answer 1

[tex]2005+2*(1+2+3+...+2004)= \\ 2005+2* \frac{2004(2004+1)}{2}= \\ 2005+2004*2005= \\ 2005(1+2004)= \\ \boxed{2005^2=p.p}[/tex]