Bonjour,
plus simple :
(Un) suite géométrique ⇒ Un+1 = qUn ⇔ q = Un+1/Un
soit q = U₉/U₈ = 30/7
U₁₀ = q x U₉ = 30/7 x 30 = 900/7
U₁₁ = q x U₁₀ = 30/7 x 900/7 = 27000/49 = 3000/7
Un = U₀ x qⁿ ⇒ U₈ = U₀ x q⁸ ⇒ U₀ = U₈/q⁸ = 7/(30/7)⁸ = 7⁹/30⁸
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Bonjour,
plus simple :
(Un) suite géométrique ⇒ Un+1 = qUn ⇔ q = Un+1/Un
soit q = U₉/U₈ = 30/7
U₁₀ = q x U₉ = 30/7 x 30 = 900/7
U₁₁ = q x U₁₀ = 30/7 x 900/7 = 27000/49 = 3000/7
Un = U₀ x qⁿ ⇒ U₈ = U₀ x q⁸ ⇒ U₀ = U₈/q⁸ = 7/(30/7)⁸ = 7⁹/30⁸