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demonstrati ca nr 9×(5+10+25+...+200)÷41 este patrat perfect

Răspuns :

9×(5+10+15+25+...+200):41 =
= 9×5×(1 + 2 + 3 + 5 +...+ 40) : 41 =
= 45 × (40×41:2) : 41 =
= 45 × 41×20:41 =
= 45 × 20 =
= 900 =
= 30^2 p.p