(8a+15a+0,5ab)×2a=(23a+0,5ab)×2a=46a+ab
B_4 = 9, q = 1/3. Найти S_5/
S_n = b_1(1 - q^n) / (1 - q) --- формула n-го члена геометрич. прогрессии.
b_4 = b_1 * q^3 ----> b_1 = b_4 / q^3 = 9 / (1/3) = 9*3 = 27/
S_5 = 27(1 - (1/3)^5 / (1 - 1/3) = 27*(1 - 1/243) /(2/3) = 27* (242/243) *(3/2) =
= 121/3 = 40 1/3
Ответ. 40 1/3
2 * (- 0.7 ) - 3 * 9.2 + 4 * 5.4 = -1.4 - 27.6 + 21.6 = - 29 + 21.6 = - 7.4