Kindly help for these simple multiple type questions

[moonnightingale]

Kindly tell me answer for these 2 questions

For second one the answer is 20 i think
what abt the first one

 

[permute]

for the first, think about superposition:
bk = ak + FT(1)

for ak = bk for all k, then the fourier transform of 1 must be all 0's. for ak != bk for all k, then the fourier transform of 1 must be non-zero for all k. for a0 = b0, then it must be zero for at least the first coefficient. for a0 != b0, then it must be non zero for at least the first coefficient.

 

[moonnightingale]

So kindly tell me answer
and am i correct for second one

Is it 20 Hz

 

[permute]

If you could come up with a guess for the second one, why not try the first. It really should be obvious at this point. what is the DFT of f[n] = 1? The DFT will match one of the four cases listed above.

 

[moonnightingale]

For me Option (b) is correct

Am i right