Question

Aratati ca numarul 9.(5+10+15....+200):41 sa fie patrat perfect !!! va dau coroana

Answer 1

9[5+10+15+...+200]/41
⇒9·5[1+2+3+...+40]/41
⇒9·5[40·41/2]/41
⇒9·5[40/2]
⇒9·5·20
⇒45·20
⇒900⇒900=30²⇒patrat perfect;