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_introanalysis_assignment_1.pdf

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t-1

Introduction to Analysis — IAUSS 2020

Assignment-1

Due: TBD

Marks

[12]

1. Answer the following questions

(a) If a and b are any two real numbers, then prove that

|a − b| ≥ ||a| − |b|| and |a + b| ≥ ||a| − |b||

(b) If a nonempty set S of real numbers is bounded below, then infS is the unique real number

α such that

m

i. x ≥ α for all x in S

ii. if > 0 (no matter how small), there is an x0 in S such that x0 < α +
(c) Find the supremum and infimum of each S. State whether they are in S
[5]
ig
n
i. S = {x|x = −(1/n) + [1 + (−1)n ]n2 , n ≥ 1}
ii. S = {x|x2 ≤ 7}
iii. S = {x||2x + 1| < 5}
2. Let n0 be any integer (positive, negative, or zero). Let Pn0 , Pn0 +1 , · · · , Pn , · · · be propositions, one for each integer n ≥ n0 , such that
(a) Pn0 is true
(b) for each integer n ≥ n0 , Pn implies Pn+1
As
s
Then prove that Pn is true for every integer n ≥ n0 .
[7]
3. (a) Find Find and prove by induction an explicit formula for an if a1 = 1 and for n ≥ 1
an
i. an+1 =
(n + 1)(2n + 1)
n
1
ii. an+1 = 1 +
an
n
(b) Prove by induction that
sin(x) + sin(3x) + · · · + sin(2n − 1)x =
[6]
1 − cos(2nx)
, n≥1
2 sin(x)
4. (a) Prove that a set T1 is denumeratble if and only if there is a bijection from T1 onto a
denumerable set T2 .
–2–
(b) Prove in detail that if S and T are denumerable, then S ∪ T is denumerable.
(c) Prove that the collection F (N) of all finite subsets of N is countable.
[30]
T. Sheel, August 7, 2018
Introduction to Analysis — IAUSS 2020
Assignment-2
Due: TBD
en
t-2
Marks
1. Let A and B be bounded nonempty subsets of R, and let A + B = {a + b : a ∈ A, b ∈ B}.
Prove that sup(A + B) = supA + supB and inf (A + B) = inf A + inf B.
[8]
2. (a) Use the definition of the limit of a sequence to establish the following limits
n
=0
i. lim
n→∞
n2 + 1
2
n −1
1
ii. lim
=
2
n→∞
2n + 3
2
√
n
iii. lim
=0
n→∞
n+1
(−1)n n
iv. lim
=0
n→∞
n2 + 1
n+1
a
+ bn+1
3. (a) If 0 < a < b, determine lim
n→∞
an + bn
a+b
p
(n + a)(n + b) − n =
(b) If a > 0, b > 0, show that lim

n→∞

2

(c) Show that if (xn ) and (yn ) are convergent sequences, then the sequences (un ) and (vn )

defined by un = max{xn , yn } and vn = min{xn , yn } are also convergent.

4. (a) Let x1 > 1 and xn+1 = 2 −

As

s

[5]

ig

n

[9]

m

[4]

the limit

1

for n ∈ N. Show that (xn ) is bounded and monotone. Find

xn

(b) Let A be an infinite subset of R that is bounded above and let u = supA. Show there

exists an increasing sequence (xn ) with xn ∈ A for all n ∈ N such that u = lim (xn ).

[4]

n→∞

5. Let X = (xn ) and Y = (yn ) be given sequences, and let the ”shuffled” sequence Z = (zn ) be

defined by z1 = x1 , z2 = y1 , · · · , z2n−1 = xn , x2n = yn , · · · . Show that Z is convergent if and

only if both X and Y are convergent and lim X = lim Y .

[30]

T. Sheel, August 7, 2018

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