Math 142B function
function
Math 142B
March 18, 2023
Final Examination v.A
(Total Points: 50)
Name:
PID:
Instructions
1. Write your Name and PID in the spaces provided above.
2. Complete the Excel with Integrity Pledge on the last page.
3. Make sure your Name is on every page you turn in.
4. No calculators, tablets, phones, or other electronic devices are allowed during this exam.
5. Put away ANY devices that can be used for communication or can access the Internet.
6. You may use one handwritten page of notes, but no books or other assistance during this exam.
7. Read each question carefully and answer each question completely.
8. Write your solutions clearly in the spaces provided.
9. Show all of your work. No credit will be given for unsupported answers, even if correct.
0.(2 points) Carefully read and complete the instructions at the top of this exam sheet and any additional
instructions written on the chalkboard during the exam.
v.A (page 2 of 9) Name:
1.(6 points) Find
lim
x→0
[
1
x
− 1
x2
log (1 + x)
]
.
Fully justify your answer.
v.A (page 3 of 9) Name:
2.(6 points) Find
lim
x→+∞
(
1− 1
x
)x
.
Fully justify your answer.
v.A (page 4 of 9) Name:
3.(6 points) Use power series to find the value of the numerical series
∞∑
n=0
1
(n+ 1) · 2n .
v.A (page 5 of 9) Name:
4.(6 points) Determine whether the following improper integral converges or diverges:∫ π
2
0
1
cos2(x) sin2(x)
dx.
v.A (page 6 of 9) Name:
5.(8 points) Suppose f : R→ R is an infinitely differentiable function such that∣∣f (k)(x)∣∣ ≤Mk+1 k! for all x ∈ R and k ∈ N
for some M > 0 where the bound is attained at x = 0 for infinitely many indices.
Recall that the Taylor series for f centered at x = 0 has the form
∞∑
k=0
f (k)(0)
k!
xk.
(a) Find the radius of convergence R ≥ 0 of the Taylor series of f centered at 0 (being an
instance of a power series).
(b) Prove that the Taylor series converges to f on (−R,R) and that the convergence is uniform
on any [−r, r] ⊂ (−R,R).
v.A (page 7 of 9) Name:
6.(8 points) Not every uniformly convergent sequence of differentiable functions (fn) defined on R converges
to a differentiable function f on R.
Consider the sequence of continuously differentiable functions (gn) defined on R by
gn(x) =
1
n
arctan(n2x).
(a) Show that (gn) converges uniformly on R to a continuous function g defined on R and
determine a formula for g(x).
(b) Show that the sequence (g′n(0)) is unbounded. Briefly explain why this implies that (g′n)
does not converge pointwise to g′ on R. [Don’t forget that arctan′(y) = 1
1+y2
.]
v.A (page 8 of 9) Name:
7.(8 points) Write the letter of the sequence in the right column in the space next to the matching description
in the left column. No justification is required. Yes, there is a sequence that will not be matched.
Each correctly placed letter (including a correctly unplaced letter) will earn one point.
A sequence of continuous functions
{fn} whose pointwise limit function f
is not continuous
A.
fn : R→ R
fn(x) =
n∑
k=0
1
k!
xk
A sequence of continuous functions
{fn} whose pointwise limit function f
is continuous but
∫ 1
0
f ̸= lim
n→∞
∫ 1
0
fn
B.
fn : [0, 1]→ R
fn(x) =
{
1 if x = k2n , k ∈ Z
0 otherwise
A sequence of polynomial functions
{fn} whose pointwise limit function f
is analytic (that is, represented by a
power series)
C.
fn : [0, 1]→ R
fn(x) = x
n
A sequence of integrable functions
{fn} whose pointwise limit function f
is not integrable
D.
fn : R→ R
fn(x) =
1
n arctan
(
n2x
)
A sequence of infinitely differentiable
functions {fn} whose uniform limit
function f is not differentiable
E.
fn : [0, 1]→ R
fn(x) =
n2x if 0 ≤ x < 1n
2n− n2x if 1n ≤ x < 2n
0 if 2n ≤ x ≤ 1
A sequence of bounded functions {fn}
whose pointwise limit function f is
unbounded
F.
fn : (−1, 1)→ R
fn(x) =
√
x2 + 1n
A sequence of noncontinuous
functions {fn} whose uniform limit
function f is continuous
G.
fn : [0, 1]→ R
fn(x) =
x
x2 + 1n
H.
fn : [−1, 1]→ R
fn(x) =
{
− 1n if − 1 ≤ x < 0
1
n if 0 ≤ x ≤ 1
Math 142B Excel with Integrity Pledge
The Excel with Integrity pledge affirms the UC San Diego commitment to excel with integrity
both on and off campus, in academic, professional, and research endeavors.
According to the International Center for Academic Integrity, academic integrity means
having the courage to act in ways that are honest, fair, responsible, respectful & trustworthy
even when it is difficult. Creating work with integrity is important because otherwise we
are misrepresenting our knowledge and abilities and the University is falsely certifying our
accomplishments. And when this happens, the UCSD degree loses its value and we’ve all
wasted our time and talents!
Name: PID:
Excel with Integrity Pledge
I am fair to my classmates and instructors by not using any unauthorized aids.
I respect myself and my university by upholding educational and evaluative goals.
I am honest in my representation of myself and of my work.
I accept responsibility for ensuring my actions are in accord with academic integrity.
I show that I am trustworthy even when no one is watching.
Affirm your adherence to this pledge by writing the following statement in the space below:
I Excel with Integrity.