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math104-f21:hw2 [2021/09/03 05:04]
pzhou created
math104-f21:hw2 [2026/02/21 14:41] (current)
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 ====== HW 2 ====== ====== HW 2 ======
-Due Tuesday Sep 7th, 6pm. +Due Thursday Sep 9th, 6pm. 
  
 In the following, a sequence $(a_n)$ means $(a_n)_{n=0}^\infty$, unless otherwise specified. You can only use properties of real number proved in Tao's book, section 5.4. In the following, a sequence $(a_n)$ means $(a_n)_{n=0}^\infty$, unless otherwise specified. You can only use properties of real number proved in Tao's book, section 5.4.
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 3. Let $(a_n)$ be a Cauchy sequence in $\Q$, and let the sequence $(b_n)$ be defined such that $b_n = a_{2n}$.  Prove that $(b_n)$ is equivalent to $(a_n)$.  3. Let $(a_n)$ be a Cauchy sequence in $\Q$, and let the sequence $(b_n)$ be defined such that $b_n = a_{2n}$.  Prove that $(b_n)$ is equivalent to $(a_n)$. 
  
-4. Tao p115Exercise 5.4.1+4. If $(a_n)$ and $(b_n)$ are Cauchy sequencesprove that $(a_n b_n)$ is also a Cauchy sequence
  
-5. Tao p116Exercise 5.4.7+5. If $(a_n)$, $(c_n)$ and $(b_n)$ are Cauchy sequences, and $(a_n) \sim (c_n)$, prove that $(a_n b_n) \sim (c_n b_n)$  
 + 
 +(Problem 4 and 5 together proves Tao proposition 5.3.10, multiplication of real are well-defined)
math104-f21/hw2.1630645452.txt.gz · Last modified: 2026/02/21 14:43 (external edit)