Odpowiedź:
a₁ = 7
a₂ = a = a₁ + r = 7 + r
a₃ = b = a₁ + 2r = 7 + 2r
a₄ = a₁ + 3r = 7 + 3r = 16
16 = 7 + 3r
3r = 16 - 7 = 9
r = 9/3 = 3
a = a₁ + r = 7 + 3 = 10
b = a₁ + 2r = 7 + 2 * 3 = 7 + 6 = 13
sprawdzenie
a₄ - b = b - a = a - a₁
16 - 13 = 13 - 10 = 10 - 7
3 = 3 = 3
Odp: a = 10 , b = 13
