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aratati ca nr a=(3^21+3^20+3^19):39 este patrat perfect

Răspuns :

Matepentrutoti
[tex]a=(3^{21}+3^{20}+3^{19}):39\\ a=3^{19}(3^2+3^1+3^0):39\\ a=3^{19}\cdot13:(13\cdot 3)\\ a=3^{19}:3=3^{18}=(3^9)^2=\ \textgreater \ \\ a=patrat\ perfect[/tex]

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