Real Analysis Notes and Exercises
Description:
This document provides comprehensive notes and exercises on key topics in Real Analysis, designed for undergraduate mathematics students. It spans three pages, covering fundamental concepts such as sequences and limits, series, and continuity. Each s...
Real Analysis Notes and Exercises
Page 1: Sequences and Limits
Notes
1. Definitions:
- Sequence: A sequence is a function from the set of natural numbers ℕ to a set S.
Typically, S ⊆ ℝ, and a sequence is written as (a_n)_{n=1}^∞ or simply (a_n).
- Limit of a Sequence: A sequence (a_n) has a limit L ∈ ℝ if for every ε > 0, there exists
a natural number N such that |a_n - L| < ε for all n ≥ N.
2. Theorems:
- Uniqueness of Limits: If a sequence (a_n) has a limit, then it is unique.
- Squeeze Theorem: If a_n ≤ b_n ≤ c_n for all n ≥ N and lim_{n → ∞} a_n = lim_{n → ∞}
c_n = L, then lim_{n → ∞} b_n = L.
3. Examples:
- Consider the sequence a_n = 1/n. We claim lim_{n → ∞} a_n = 0.
- Given ε > 0, choose N = ⌈1/ε⌉. For n ≥ N, 1/n ≤ 1/N < ε.
2. 2. Show that the sequence a_n = (-1)^n does not have a limit.
Solution:
a_n = (-1)^n alternates between 1 and -1.
For the limit to exist, the sequence must converge to a single value, but here it does not.
3. 3. Determine whether the sequence a_n = √(n+1) - √n converges and find its limit if it
does.
Solution:
a_n = √(n+1) - √n = (√(n+1) - √n)(√(n+1) + √n)/(√(n+1) + √n) = 1/(√(n+1) + √n)
lim_{n → ∞} a_n = lim_{n → ∞} 1/(√(n+1) + √n) = 0
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