10 例题3-11 x(t)=2 cos 6It +4 sin 10rt f,=8<2fm 解:②=8点周期时采样周期2==8=1 个周期内采样点数N=0=8甚基本频率9 采样信号x2(n)=x(0)1=m2=26+4sm00 2( 3n)+sin(5-n) 4 2 cos(3-n)-4sin(3-n) X2(92)=∑x2(m) 82 2 1 1 , 8 s s T f = = 例题3－11 10 5 2 2 m m f     = = = 0 T =1 2 2 ( ) ( ) |t nT x n x t = = 1 8 2 s m f f =  2 4 7 2 0 2 0 1 ( ) ( ) 8 jk n n X k x n e  − =   =   解： ② fs1=8点/周期时采样周期 一个周期内采样点数 0 2 8 s T N T = = 基本频率 02 2 N 4    = = 采样信号 2cos(6 ) 4sin(10 ) 8 8 n n = +   x t t t ( ) 2cos 6 4sin10 = +   2cos(3 ) 4sin(5 4 4 n n)   = + 2cos(3 ) 4sin(3 4 4 n n)   = − 0 X k( ) 