Prove that both of the following sequences are Cauchy sequences, using just the definition (not any Theorems.) (a) {4"} (b) {„}, (-1)" | n-1 n+1

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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use the method in second image example 20.2

Prove that both of the following sequences are Cauchy sequences, using just the definition (not any Theorems.)
(a) {"}°
n=1
8.
(b) {까1Sn=1
n+1
Transcribed Image Text:Prove that both of the following sequences are Cauchy sequences, using just the definition (not any Theorems.) (a) {"}° n=1 8. (b) {까1Sn=1 n+1
lam – an| =-
Example 20.2. I claim the sequence {÷} is a Cauchy sequence.
Proof. Pick e > 0. (Scratch work: we need to figure out how big m
and n need to be in order that -< e. Note that if both and 1
are between 0 and ɛ, then the distance between them will be at most
ɛ, and this occurs so long as n, m >!. So we will set N = !. Back to
the proof.) Let N = !. Let m, n eN be such that m > N and n > N.
Then 0 < < = e and 0 < 습 <★
m
%3D
= €. It follows that
m
1
1
lam – an
and this proves the sequence is Cauchy.
Transcribed Image Text:lam – an| =- Example 20.2. I claim the sequence {÷} is a Cauchy sequence. Proof. Pick e > 0. (Scratch work: we need to figure out how big m and n need to be in order that -< e. Note that if both and 1 are between 0 and ɛ, then the distance between them will be at most ɛ, and this occurs so long as n, m >!. So we will set N = !. Back to the proof.) Let N = !. Let m, n eN be such that m > N and n > N. Then 0 < < = e and 0 < 습 <★ m %3D = €. It follows that m 1 1 lam – an and this proves the sequence is Cauchy.
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