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ELEC211Si l dS t
ELEC 211 Signals and Systems

Review Short Questions
Chapters 1-55

Chapters 1
Albert Wongg


Chapters 1 2

Chapters 1 --2

Question 1 -Which of the following is NOT a
compp
lex sinusoid?

. jt
(a) () () = ee 8
(a) xtxt
1
. (2 + j )t
(b) xt() = e 8
(b) () 8
j2 n
j
(c) (c) xnxn[] =
[] ee

j(( 2 + ) n
(d) [] = ej 3)
xn
The Hong Kong University of Science and Technolog
Department of Electrical and Electronic Engineering



Question 3 Which of the following is correct if
y[n]=w[[
n]*[[
nn--33]?

y[]] ]
aa.
y[n]=w[3]

y[n]=w[3]
b y[n]y[n]=w[n+3]

b.
w[n+3]

c.
y[n]=w[n3]
y[n]=w[n--3]
d. y[3]=1, otherwise =0


The Hong Kong University of Science and Technolog
Department of Electrical and Electronic Engineering

Question 4 -Which of the following impulse response
is causal AND stable?


hh((tt)) hh((tt))
(c)

h(t)(a) (b)
tt t

t



Chapters 1-2 -Answers

Chapters 1 2 Answers

1.
(b) C it is a general complex exponential; Also, (c) is

(b) Cit is a general complex exponential; Also, (c) is not strictly speaking periodic C it is something that
we will not encounter in this course and it is not
par
ticticu
llarl
ly
meaningfmeaningful
l tto
discdiscuss it
it

2. (d)

33.
()

(c)

4. (b)
5 ()(a) C th
the
iintegral on
ththe RHS is a
ffuncti
tion o
ff . It
It

5.
l RHSi
integrates away t.


Chapter 3

QuestionQuestion 11 --What is the FS of
cosot ?

11
(a)
a = , a =. , and a = 0,for k 1,.1
1 .1 k
2 j 2 j

11

(b)
a1 = , a. =. , and a = 0,for k 1,.1
2 122 k

2
(c)
a = 1, a = 1 , and a = 0,for k 1,.1
(c)
11 .11 kk
2 j 22 j
2 jj
(d)(d)
a 12 , a.1 = 12 and aa = 00,forfor k 1 .1
a = a , and k 1, 1
1 k

The Hong Kong University of Science and Technolog
Department of Electrical and Electronic Engineering

Question 2 -
Which of the following is a valid

Which of the following Fourier Series analyy
sis eqq
uation?

. jk t
(a) ()) = akk 8
() xt( e
k
3
13 . jj t
1 88
(b) a = x(t)e ddt
(b) 33 ()
0
1
1
1 16. jt
(c) a4 = x() 2
te dt
0
16
92
. jk n
() xn e 8
(d) [] = akk
k = 2

The Hong Kong University of Science and Technolog
Department of Electrical and Electronic Engineering


Question 3 -What is the FS coefficients of

Question 3 What is the FS coefficients of
the shifted periodic impulse train

xt = t .nT .
()( )
n=.
(a)
ak =1/T

(b)
ak (1


=.)/ T
2
.jk
(c)
akk =eT / T

(d)
ak =1/(T .)



The Hong Kong University of Science and Technolog
Department of Electrical and Electronic Engineering

Question 4 C x[n] has a period of N and is real

Question 4 x[n] has a period of N and is real,
and let ak be its FS coefficients. Which of the

and let a
following statements is not necessarily true?

f