2. Let {an} be a decreasing sequence of positive numbers with limit 0. I define a new sequence {xn} as follows: n=1 n=1 X1 = a1 Vn E Zt, Xn+1 = Xn + (-1)"an+1 Prove that the sequence {xn}1 satisfies the hypotheses of Lemma A, and hence is it con- vergent.

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
Section: Chapter Questions
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Please do #2 but refer to #1 for Lemma A

2. Let {an} be a decreasing sequence of positive numbers with limit 0. I define a new
sequence {xn}n=1 as follows:
=D1
100
X1 = a1
Vn E Zt, Xn+1 = Xn + (-1)"an+1
Prove that the sequence {xn} satisfies the hypotheses of Lemma A, and hence is it con-
vergent.
This question is quite long and you will need to prove a few different things. Before you
start, make a strategy. Decide what the various things you need to prove are, and in which
order. Begin the proof by writing a summary of the steps you are going to take. Make sure
your reader understands where in your proof you are at each moment. Make your proof as
easy to read as you would like it to be if you were reading it for the first time
yourself.
Suggestions: You do not need to write a single e! Use the theorems you have learned in Unit
11 instead. Before you start, as rough work, write explicitly an equation for the first few x's
in terms of the first few a's to make sure you understand the definition. Draw the numbers
X1, X2, X3, X4, X5, X6, x7, and x8 in a real line and order them. You will notice that the
sequences {En}n=1 and {On}n=1 appear to satisfy certain properties which will be helpful in
your proof. Of course, anything you want to use in your proof needs to be proven first.
Transcribed Image Text:2. Let {an} be a decreasing sequence of positive numbers with limit 0. I define a new sequence {xn}n=1 as follows: =D1 100 X1 = a1 Vn E Zt, Xn+1 = Xn + (-1)"an+1 Prove that the sequence {xn} satisfies the hypotheses of Lemma A, and hence is it con- vergent. This question is quite long and you will need to prove a few different things. Before you start, make a strategy. Decide what the various things you need to prove are, and in which order. Begin the proof by writing a summary of the steps you are going to take. Make sure your reader understands where in your proof you are at each moment. Make your proof as easy to read as you would like it to be if you were reading it for the first time yourself. Suggestions: You do not need to write a single e! Use the theorems you have learned in Unit 11 instead. Before you start, as rough work, write explicitly an equation for the first few x's in terms of the first few a's to make sure you understand the definition. Draw the numbers X1, X2, X3, X4, X5, X6, x7, and x8 in a real line and order them. You will notice that the sequences {En}n=1 and {On}n=1 appear to satisfy certain properties which will be helpful in your proof. Of course, anything you want to use in your proof needs to be proven first.
1. Prove the following lemma:
Lemma A. Let {xm} be a sequence of real numbers. We define two new
n=1
sequences {En} and {On} as:
n=1
n=1
Vn E Z+, En
Vn E Zt, On = x2n-1
= X2n,
%3D
• IF the sequences {En}
• THEN the sequence {xn}=1 is also convergent.
100
}n=1
and {On}1 are both convergent to the same limit,
n=1
Suggestion: Use the definition of limit.
Transcribed Image Text:1. Prove the following lemma: Lemma A. Let {xm} be a sequence of real numbers. We define two new n=1 sequences {En} and {On} as: n=1 n=1 Vn E Z+, En Vn E Zt, On = x2n-1 = X2n, %3D • IF the sequences {En} • THEN the sequence {xn}=1 is also convergent. 100 }n=1 and {On}1 are both convergent to the same limit, n=1 Suggestion: Use the definition of limit.
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