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Aratati ca (2 la puterea 2n+1 inmultit cu 5 la puterea n plus 4 la puterea n inmultit cu 5 la puterea n+1 ) se imparte exact la 7

Răspuns :

[tex] {2}^{2n + 1} \times {5}^{n} + {4}^{n} \times {5}^{n + 1} [/tex]

[tex] = {2}^{2n + 1} \times {5}^{n} + {2}^{2n} \times {5}^{n + 1} [/tex]

[tex] = {2}^{2n} \times {5}^{n} (2 + 5)[/tex]

[tex] = {2}^{2n} \times {5}^{n} \times 7 \: \: \: \vdots \: \: \: 7[/tex]