Răspuns:
[tex]2020+2(1+2+3+...+2019)=2020+2\cdot\frac{2019\cdot2020}{2}=>\\2020+2019\cdot2020=>\\2020\cdot2020=>\sqrt{2020\cdot2020} =2020[/tex]
deci 2020+2(1+2+3+...+2019) este patrat perfect
