решение смотри на фотографии
bn = 0.8*2^n
A)
b1 = 0.8*2¹ = 1.6
b4 = 0.8*2⁴ = 0.8 * 16 = 12.8
b4 = b1q³
q³ = b4/b1
q³ = 12.8/1.6
q³ = 8
q = 2
B)
Sn = b1(q^n - 1) / (q - 1)
S4 = 1.6 * (2⁴ - 1) / 1 = 1.6 * 15 = 24
решение смотри на фотографии
bn = 0.8*2^n
A)
b1 = 0.8*2¹ = 1.6
b4 = 0.8*2⁴ = 0.8 * 16 = 12.8
b4 = b1q³
q³ = b4/b1
q³ = 12.8/1.6
q³ = 8
q = 2
B)
Sn = b1(q^n - 1) / (q - 1)
S4 = 1.6 * (2⁴ - 1) / 1 = 1.6 * 15 = 24