Math 0420 Exam 1 Practice Problems
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Exam 1 Practice Problems
1. Suppose that f : S → R and c is a cluster point of S .
(a) Show that if x(l)f (x) exists, then x(l)|f (x)| exists.
(b) Suppose that x(l)|f (x)| exists. Give an example to show that x(l)f (x) may not exist.
2. Prove that the function f defined by f (x) = 1 + x if x is rational and f (x) = 1 - x if x is irrational is continuous only at 0.
3.
(a) Show that there exists a real number x > 2π such that tan x = x. Make sure to state and justify the use of any theorems that you use.
(b) Give an example of a function f : (-1, 1) → R such that f is not continuous on (-1, 1), but f satisfies the conclusion of the Max-Min Theorem.
4. Prove, by definition, that f (x) = 4/x2 is uniformly continuous on (2, 5].
5. Prove or give a counterexample for the following statement:
If {xn } is a bounded sequence, and k is any constant, then lim sup (kxn ) = n →o
│ 、
6. For each of the following, indicate whether the statement is True or False. Give a brief explanation for your choice or a counterexample in each case.
(a) If A c S c R and c is a cluster point of S, then c is also a cluster point of A.
(b) If {xn }n–(o)1 S [a, b], then {xn }n–(o)1 has a subsequence that is a Cauchy se- quence.
(c) If lim f (x) exists, and lim g(x) does not exist, then lim (f (x) + g(x)) does x →c x →c x →c
not exist.
2023-02-07