Odpowiedź:
a₁ = - 5
[tex]r = \frac{2}{7}[/tex]
a₅₀ = ?
S₅₀ = ?
aₙ = a₁ + (n - 1)r
[tex]a_{50} = -5 + (50 - 1)*\frac{2}{7} = - 5 + 49 * \frac{2}{7} = -5 + 14 = 9[/tex]
[tex]S_{50} = \frac{2a_{1} + (n - 1)r}{2}*n[/tex]
[tex]S_{50} = \frac{2*(-5) + (50 - 1)*\frac{2}{7}}{2}*50 = \frac{-10+49*\frac{2}{7}}{2}*50 = \frac{-10+14}{2}*50 = 2*50 = 100[/tex]
a₅₀ = 9
S₅₀ = 100