Ответ:
b1 =
Объяснение:
q=1/3
S5 = 27_2/3 = 83/3
b1 - ?
S = b1 * (q^(n) - 1 ) / (q-1)
S5 = b1 *(q^5 - 1) / (q - 1) = b1 * (1/243 - 1) / (-2/3) = - b1 * (-242/243) *3/2 =
= b1 * 121 / 81
83/3 = b1 * 121/81
b1 = 83 /3 : 121/81
b1 = 83/3 * 81/121
b1 = 83*27 / 121 = 2241 /121 = 18_63/121