151. Which one of the following input -output relationship is that of a linear system?

1. 1. 

   
   
   

   2. 

   
   
   

   3. 

   
   
   

   4. 

   
   
   

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   NA

   Correct Option: D

   NA

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152. If a(n) is the response of a linear, time-invariant, discrete-time system to a unit step input, then the response of the same system to a unit impulse input is

1. 1. d/dn [a(n)]

   
   
   

   2. na (n)

   
   
   

   3. a(n) – a(n – 1)

   
   
   

   4. a(n + 1) – 2a(n) + a(n – 1)

   
   
   

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   NA

   Correct Option: A

   NA

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153. Which of the following transfer function of second order li near time-invariant systems, the underdamped system is represented by

1. 1. H(s) =	1
      	s² + 4s + 4

   
   
   

   2. H(s) =	1
      	s² + 5s + 4

   
   
   

   3. H(s) =	1
      	s² + 4.5s + 4

   
   
   

   4. H(s) =	1
      	s² + 3s + 4

   
   
   

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   ζ 0.75 < A (Under damped)

   Correct Option: D

   ζ 0.75 < A (Under damped)

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154. Which one of the following system is non-linear?
     [y(t) = output; x(t) = input]

1. 1. y(t) = 2x(t – 1) – 3x(t – 2) + x(t – 3)

   
   
   

   2. y(t) = 5x(t)

   
   
   

   3. y(t) = 2x(t – 1) – 3x(t – 2) – x(t – 3)

   
   
   

   4. y(t) = 2x(t) + 3.6

   
   
   

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   Correct Option: A

   

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155. The Z-transform of a anti causal system is
     

     X(z) =	12 - 21z
     	3 - 7z + 12z²

     
     The value of x[0] is

1. 1. – 7/4

   
   
   

   2. 0

   
   
   

   3. 4

   
   
   

   4. none of these

   
   
   

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   Correct Option: C

   
   

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