已知两个序列x[n]=cos(n*pi/2), y[n]=ej*pi*n/4x[n],绘制X(ejw)和Y(ejw)和幅度和相角,说明它们的频移关系-The known two sequence x [n] = cos (n* PI/2), y [n] = ej* PI* n/4 x [n], draw x (ejw) and y (ejw) and amplitude and phase Angle, suggesting their frequency shift relationship