信号与系统2012-2013试题参考答案
一 、PART 1 CHOOSING THE BEST ANSWER (30 points) (Arrange the answers for all questions into the following Table.) Question 1Answer
C
6B
7C
8A
9A
10A
PART 2 ANSWER THE FOLLOWING QUESTIONS (40 points) 1.
1, for t /2
Use the definition X( ) x(t)e j tdtto compute the Fourier A Signal is p(t)
0, for all other t
transform P( )and sketch the amplitude spectrumP( ).
Answer: X( )
x(t)e
j t
2
dt
e
2
j t
j j 1 2
dt e2) sinc(e
j 2
2. Determine whether the continuous-time system is causal or noncausal, has memory or is
memoryless, linear or nonlinear, time varying or time invariant, give out your reasons.
y(t) (t )x( )d
0t
Answer: the system is causal, has memory, linear and time varying.
3. For the discrete-time signals x[n]and [n], which are given in the following, compute the
convolution x[n] [n]for n 2.
x[n] 1 for 1 n 2and x[n] 0 for all other integers n;
[ 1] 1, [0] 0, [1] 8, [2] 2, [3] 3,and [n] 0for all other integers n.
Answer:
