Unformatted text preview: Mock ﬁnal test.
1. List all limit points, supremum and inﬁmum of the sequence (sin(πnq)) where q is a ﬁxed
rational number. What happens for an irrational q?
2. Let (xn ) be a sequence of points in a metric space X that converges to a point x. Show
that it has a subsequence converging as fast as you please. In other words, if (rk ) is any
sequence of decrreasing positive numbers that tends to 0, then you can choose a subsequence
(xnk ) so that
d(xnk , x) < rk for all k ∈ IN.
3. Suppose f is a uniformly continuous mapping of a metric space X into a metric space Y .
Prove that (f (xn )) is a Cauchy sequence in Y if (xn ) is a Cauchy sequence in X.
4. Prove that the series ∞ nx (−1)
n=1 2 +n
n2 converges uniformly in every bounded interval, but does not converge absolutely for any
value of x (x is meant to be real).
5. Show that deleting the terms 1/n for all n having digit 9 in its decimal expansion makes
the harmonic series n 1/n converge.
6. Suppose f is twice-diﬀereniable on (0, ∞), f is bounded on (0, ∞), and f (x) → 0 as
x → ∞. Prove that f (x) → 0 as x → ∞.
7. Suppose α increases monotonically on [a, b], g is a continuous real-valued function and
g(x) = G (x) for all x ∈ [a, b]. Prove that
b b α(x)g(x)dx = G(b)α(b) − G(a)α(a) −
a 8. Let (fn ) be a sequence of continuous functions which converges uniformly to a function f
on a set E. Prove that
lim fn (xn ) = f (x)
for every sequence of points xn ∈ E such that xn → x ∈ E. Is the converse of this true? ...
View Full Document
- Spring '09
- Topology, Metric space, Cauchy sequence, uniformly continuous mapping