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David24
a fost răspuns

aratati ca nr 9*(5+10+15+...+200):41 este patrat perfect.
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Răspuns :

Ctinamaria31xxx
5(1+2+3+....+40)=
5*40*41/2 = 
5*20*41

introducem in ecuatie
9*5*20*41:41=
9*5*20=
900 => patrat perfect (30^2)
Renatemambouko
9×(5+10+15+...+200):41=
=9×5×(1+2+3+...+40):41=
=45×(40+1)×40/2:41=
=45×41×20:41=
=45×20=900=30² deci patrat perfect

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