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If x(n)=xR(n)+jxI(n) is a complex sequence whose Fourier transform is given as X(ω)=XR(ω)+jXI(ω), then what is the value of xI(n)?(a) \(\frac{1}{2π} \int_0^{2π}\)[XR(ω) sinωn+ XI(ω) cosωn] dω(b) \(\int_0^{2π}\)[XR(ω) sinωn+ XI(ω) cosωn] dω(c) \(\frac{1}{2π} \int_0^{2π}\)[XR(ω) sinωn – XI(ω) cosωn] dω(d) None of the mentionedThis question was addressed to me at a job interview.My question comes from Properties of Fourier Transformfor Discrete Time Signals topic in division Frequency Analysis of Signals and Systems of Digital Signal Processing |
Answer» RIGHT option is (a) \(\frac{1}{2π} \int_0^{2π}\)[XR(ω) sinωn+ XI(ω) cosωn] dω Explanation: We KNOW that the INVERSE transform or the synthesis equation of a signal x(n) is given as x(n)=\(\frac{1}{2π} \int_0^{2π}\) X(ω)e^jωn dω By substituting e^jω = cosω + jsinω in the above equation and separating the real and imaginary parts we get xI(n)=\(\frac{1}{2π} \int_0^{2π}\)[XR(ω) sinωn+ XI(ω) cosωn] dω |
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