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Consider the sequence {an} given by an=4n4n−1, with n=1,2,3,… a) Is the sequence {an} monotone? Justify your answer. b) Show that the sequence {an} converges.

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Answer:

a) To determine if the sequence {an} is monotone, we need to check if it is either increasing or decreasing.

Let's calculate the values of the first few terms of the sequence to observe any patterns:

a₁ = 4(1) / (4(1) - 1) = 4/3 ≈ 1.333

a₂ = 4(2) / (4(2) - 1) = 8/7 ≈ 1.143

a₃ = 4(3) / (4(3) - 1) = 12/11 ≈ 1.091

From the calculated values, we can see that the sequence is decreasing. As the value of n increases, the terms of the sequence decrease.

Therefore, the sequence {an} is monotone decreasing.

b) To show that the sequence {an} converges, we need to prove that it approaches a finite limit as n approaches infinity.

Let's rewrite the expression for the nth term of the sequence {an}:

an = 4n / (4n - 1)

As n approaches infinity, the term 4n-1 in the denominator becomes negligible compared to 4n.

Therefore, as n gets larger and larger, the value of an approaches 4.

We can demonstrate this by taking the limit of the sequence as n approaches infinity:

lim(n→∞) (4n / (4n - 1)) = 4

Since the limit of the sequence is a finite number (4), we can conclude that the sequence {an} converges.

User Akshay Misal
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