Răspuns:
Explicație pas cu pas:
x₃+x₅ = 18
x₂+x₄ = 27 <=>
x₁·q²+x₁·q⁴ =18
x₁·q + x₁·q³ = 27 <=>
x₁q²·(1+q²) = 18
x₁q·(1+q²) = 27 =>
q = 18/27⁽⁹ => q = 2/3
x₁·2/3·(⁹⁾1+4/9) = 27 <=>
x₁·2/3·13/9 = 27 <=>
x₁·26/27 = 27 => x₁ = 729/26
x₂ = x₁q = 726/26 ·2/3 = 243/13
x₃ = x₂q = 243/13 ·2/3 = 162/13
x₄ = x₃q = 162/13 ·2/3 = 108/13
x₅ = x₄q = 108/13 ·2/3 = 72/13
x₂+x₄ = (243+108)/13 = 351/13 = 27
x₃+x₅ = (162+72)/13 = 234/13 = 18, corect
