GATE EC 2015 Set 1 — Question 53
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Signals & Systems → Discrete-Time Signals → DFT & FFT
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Question
Two sequences and are related as,If another sequence is derived as,then the relationship between the sequences and is
Correct answer
(C) [p,q,r] = [c, a, b]
Solution
Let the first transformation be , where , , andGiven . We know .
So, , , .
Substituting these into :This matrix is the inverse Discrete Fourier Transform (IDFT) matrix, scaled by . Specifically, .
So, . This implies .
From this, the components of are:
Now consider the second transformation , where andAgain, using , we have .
So, becomes:Notice that .
So, .
Substituting into the definition of for :
Now, let's compare with :
We found:
And for :
Therefore, the relationship between the sequences is .The final answer is
So, , , .
Substituting these into :This matrix is the inverse Discrete Fourier Transform (IDFT) matrix, scaled by . Specifically, .
So, . This implies .
From this, the components of are:
Now consider the second transformation , where andAgain, using , we have .
So, becomes:Notice that .
So, .
Substituting into the definition of for :
Now, let's compare with :
We found:
And for :
Therefore, the relationship between the sequences is .The final answer is
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