Question

Aratati ca numarul 9 x(5+10+15+...+200):41 este patrat perfect.

Answer 1

9X5(1+2+...........+40):41=
45.(1+40).20:41=45.41.20:41=
45.20=900=30²
DECIESTE PATRAT PERFECT

Answer 2

$9 \cdot (5+10+15+...+200):41= \\ \\ =9 \cdot 5(1+2+3+...+40):41= \\ \\ =45 \cdot \frac{40 \cdot 41}{2}:41= \\ \\ =45 \cdot 20= \\ \\ =900= \\ \\ =30^2-patrat~perfect$