Найти сумму первых пяти членов прогрессии если 1) в4=88 q=2 2) в1=11 в4=88

1) b4 = b1* q³ , отсюда b1 = b4 : q³ = 88 : 2³ = 88 : 8 = 11
    S5 = [b1(q^5 - 1)] / (q - 1) = [11(2^5 - 1)] / (2 - 1) = 11 * (32 - 1) =
    = 11 * 31 = 341
2) b4 = b1*q³ , отсюда q³ = b4 : b1 = 88 : 11 = 8       q = 2
S5 = [b1(q^5 - 1)] / (q - 1) = [11(2^5 - 1)] / (2 - 1) = 11 * (32 - 1) =
    = 11 * 31 = 341