Odpowiedź:
Dodatnie wyrazy tego ciągu to: a₃, a₄, a₅.
Szczegółowe wyjaśnienie:
[tex]a_{n} = -n^{2}+8n-12\\\\-n^{2}+8n-12 > 0\\\\\Delta=b^{2}-4ac = 8^{2}-4\cdot(-1)\cdot(-12) = 64-48 = 16\\\\\sqrt{\Delta} = \sqrt{16} = 4\\\\n \in N_+\\\\n_1 = \frac{-8+4}{-2} = \frac{-4}{-2} = 2\\\\n_2 = \frac{-8-4}{-2} = \frac{-12}{-2} =6\\\\a = -1 < 0, to \ ramiona \ paraboli \ skierowane \ do \ dolu\\\\n \in (2;6)\\\\n \in \{3,4,5\}[/tex]
