Odpowiedź:
a₁ = 2x + 1
a₂ = 61
a₃ = 6x + 1
a₃ - a₂ = a₂ - a₁
6x + 1 - 61 = 61 - 2x - 1
6x - 60 = - 2x + 60
6x + 2x = 60 + 60 = 120
8x = 120
x = 120 : 8 = 15
a₁ = 2 * 15 + 1 = 30 + 1 = 31
a₂ = 61
a₃ = 6 * 15 + 1 = 90 + 1 = 91
sprawdzenie
91 - 61 = 61 - 31
30 = 30
L = P
r - różnica ciągu = a₂ - a₁ = 61 - 31 = 30
an = a₁ + (n - 1) * r = 31 + (n - 1) * 30 = 31 + 30n - 30 = 30n + 1
