Question

23 БАЛЛА!
ОЧЕНЬ ПРОШУ, СПАСИТЕ МЕНЯ!!!
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Answer 1

г)

b₁ + b₂ + b₃ = 7

b₁b₂b₃ = 8

bₙ = b₁ qⁿ⁻¹

b₁ * b₁q * b₁q² = b₁³ q³ = 8

b₁q = 2

b₁ + b₁q + b₁q² = b₁ + b₁q + b₁q*q = b₁ + 2 + 2q = 7

b₁ + 2q = 5

b₁ = 5 - 2q

(5 - 2q)q = 2

2q² - 5q + 2 = 0

D = 25 - 16 = 9

q₁₂ = (5 +- 3)/4 = 2 и 1/2

1. q = 2  b₁ = 5 - 2q = 5 - 4 = 1

2. q = 1/2 b₁ = 5 - 1 = 4

б)

b₂ = 10

b₃ + b₄ = 60

b₃ = b₂q

b₄ = b₃q = b₂q*q = b₂q²

b₂q + b₂q² = 10(q + q²) = 60

q² + q - 6 = 0

D = 1 + 24 = 25

q₁₂ = (-1 +- 5)/2 = 2 и -3

1. q = 2  b₂ = b₁q = 2b₁ =  10   b₁ = 5

2. q=-3  b₂ = b₁q = -3b₁ = 10   b₁ = - 10/3