1. The problem statement, all variables and given/known data Hi, I need to find the Fourier Transform of: g(t) = (e^-t)Sin(Wct)u(t) where Wc=2πFc and u(t) is the step function which is equal to 1 if time is +ve and 0 otherwise. 2. Relevant equations I know that g(t) = (e^-t)[e^jWct - e^-jWct]/2j = [e^-t(1+jWc) - e^t(-1-jWc)]/(2j) (0<=t<=∞, because of step function u(t)) 3. The attempt at a solution Therefore the Fourier Transform would be: [1/(2j)]*∫([e^-t(1+jWc) - e^t(-1-jWc)])(e^-jWt)dt = [1/(2j)]*∫([e^-t(1-jWc+jW) - e^t(-1-jWc-jW)])dt (limits: t=∞ to t=0) = [1/(2j)][(e^-t(1-jWc+jW))/(-(1-jWc+jW)) - (e^t(-1-jWc-jW))/(-1-jWc-jW)] (sub in: t=∞ to t=0) If you sub t=+/-∞, the exponential could be 0 or it could be infinite depending on whether 1-jWc+jW and -1-jWc-jW are -ve or +ve. How can we know if they are positive or negative? Hope you guys can help! David.