Odpowiedź:
a₁ = 18
a₂= a₁q = 18q = 6
18q = 6
q = 6/18 = 1/3
S₆ = [a₁(1 - q⁶)/(1 - q) = {18[1 - (1/3)⁶]}/(1 - 1/3) = [18 * (1 - 1/1/729)/(2/3) =
= (18 * 728/729)/(2/3) = 13104/729 : 2/3 = 13104/729 * 3/2 =
= 6552/729 * 3 = 6552/243 = 26 234/243 = 26 78/81 = 26 26/27
