Răspuns:
Explicație pas cu pas:
b₁-b₂ = 8
b₂+b₃ = 12
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b₁-b₁q = 8
b₁q+b₁q² = 12
b₁(1-q) = 8 => b₁ = 8/(1-q)
b₁q(1+q) = 12 =>
8q(1+q) = 12(1-q) =>
2q+2q² = 3-3q =>
2q²+5q-3 = 0 =>
q₁,₂ = [-5±√(25+24)]/4
q₁,₂ = (-5±7)/4
q₁ = -3 ; q₂ = 1/2
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q₁ = -3 => b₁ = 2
q₂ = 1/2 => b₁ = 16
