3-1 离散傅里叶级数(6)

2 11 ( k 1 ) n j ( k 11) n 1 11 j 2 1~ 12 12 X (k ) e e 2 n 0 2 n 0

x ( n ) cos n 6~N=12

1 1 e 1 1 e 2 2 j ( k 1 ) j ( k 11) 2 2 12 12 1 e 1 e 6, k 1 12r 6, k 11 12r 0,其它的k 6, k 1 12r 6

j

2 ( k 1 ) 12 12

j

2 ( k 11) 12 12

~ X ( k ) 6, k 11 12r 0,其它的k

-2 -1 0 1 2

11 12

n

-2 -1 0 1 2

11 12

k