Răspuns:
Explicație pas cu pas:
9ˣ⁺¹-1 = 3ˣ -3ˣ⁺² <=>
(3²)ˣ⁺¹ -1 = 3ˣ - 3²·3ˣ <=>
3²ˣ⁺²-1 = 3ˣ - 9·3ˣ <=>
9·3²ˣ-1 = 3ˣ(1-9) <=>
9·3²ˣ + 8·3ˣ-1 = 0
3ˣ = t =>
9t² + 8t -1= 0 <=>
t₁,₂ = [-8±√(64+36)]/18
t₁,₂ = (-8±10)/18
t₁ = -1 ; t₂ = 1/9
t₁ = -1 => 3ˣ = -1 => nu are solutii
t₂ = 1/9 => 3ˣ = (1/3)² = 3⁻² => x = -2
