Question

дана геометрическая прогрессия bn вычислите сумму 2 первых членов b3=2/9 q=-1/3

Answer 1

b3 = b2•q => b2 = b3/q
b2 = (2/9)/(-1/3) = -6/9 = -2/3
b2 = b1•q => b1 = b2/q
b1 = (-2/3)/(-1/3) = 6/3 = 2
S2 = b1 + b2 = 2 - 2/3 = 6/3 - 2/3 = 4/3.