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Problem 1:
Let (sn ) be a sequence of real numbers.
1. Give the definition of limsupsn.
2. Let X be the set of real numbers defined as follows: x ∈ X if and only if there is N such that x > sn for n > N. In other words, X consists of the upper bounds of the tails of (sn ). Prove that limsupsn = infX .
Problem 2:
Compute the domain of convergence of the power series , i.e. the set of all x ∈ R for which the power series converges.
Problem 3:
Let S,T be non-empty subsets of R with the property that s < t for all s ∈ S and all t ∈ T. Prove that supS and infT exist and satisfy the relationsupS ≤ infT. It it also true that supS < infT? Give a proof or a counterexample.
Problem 4:
1. Given an open interval I ⊂ R and a smooth function f : I → R, define the Taylor series of f at c ∈ (a,b).
2. Compute the Taylor series of sin(x) at 0 and show that it represents sin(x) on the entire domain R.
Problem 5:
Let f : [a,b] → R be a function. Assume that there exists a sequence (hn ) of step functions hn : [a,b] → R converging uniformly to f. Show that f is integrable, without appealing to the theorem about uniform convergence and integrability proved in class.
Problem 6:
Show that for all x ≥ 0 we have sin(x) ≤ x.