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Ch. 10 - Infinite Sequences and Series
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 10, Problema 10.1.105

Recursively Defined Sequences
In Exercises 101–108, assume that each sequence converges and find its limit.
a₁ = 5,aₙ₊₁ = √(5aₙ)

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Identify the recursive sequence given: \(a_1 = 5\) and \(a_{n+1} = \sqrt{5a_n}\). We want to find the limit \(L\) as \(n\) approaches infinity, assuming the sequence converges.
Assuming the sequence converges to a limit \(L\), then both \(a_n\) and \(a_{n+1}\) approach \(L\). So, set \(L = \sqrt{5L}\) to find the limit.
Square both sides of the equation to eliminate the square root: \(L^2 = 5L\).
Rearrange the equation to standard polynomial form: \(L^2 - 5L = 0\).
Factor the equation: \(L(L - 5) = 0\). The possible limits are \(L = 0\) or \(L = 5\). Use the initial term and the nature of the sequence to determine which limit is valid.

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Recursively Defined Sequences

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Convergence of Sequences

A sequence converges if its terms approach a specific finite value as n approaches infinity. Determining convergence often involves finding a limit L such that the sequence terms get arbitrarily close to L, which is essential for solving limit problems in recursive sequences.
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Finding Limits of Recursive Sequences

To find the limit of a convergent recursive sequence, assume the limit exists and set L equal to the limit of both aₙ and aₙ₊₁. Then solve the resulting equation, often involving algebraic manipulation, to find the value of L that satisfies the recursive definition.
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