Xk=sum xn*e^{-i*2*pi*k*n/N}N=4X1=x0*e^{-i*2*pi*1*0/4}+x1*e^{-i*2*pi*1*1/4}+x2*e^{-i*2*pi*1*2/4}+x3*e^{-i*2*pi*1*3/4}=1+2*e^{-i*pi/2}+5*e^{-i*pi}+4*e^{-i*3pi/2}=1+2(-i)+5(-1)+4(i)=-4+2i同理X2=x0*e^{-i*...