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


Răspuns :

9x(5+10+15+....+200):41=
=9x5(1+2+3+....+40):41=
=9x5x40(40+1):2 :41=
=9x5x40:2 =
=900=30²
 [tex]9\cdot5*(1+2+3+...+40):41=9\cdot5\cdot\frac{4o\cdot\not41}{2}:\not41[/tex]=9*5*2o=(3*10)²=900.