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aratati ca nr N=2005+2×(1+2+3+....+2004) este patratul unui numar perfect

Răspuns :

1+2+3+...+2004=(2004×2005)/2=2005×1002
N=2005+2×1002×2005
N=2005+2004×2005
N=2005(1+2004)
N=2005×2005
N=2005^2 pătrat perfect