xa1(t)=cos(2*pi*t)
1xa1
-1-1
-0.8
-0.6
-0.4
-0.2
00.2t
xa2(t)=-cos(6*pi*t)
0.4
0.6
0.8
1
1xa2
-1-1
-0.8
-0.6
-0.4
-0.2
00.2t
xa3(t)=cos(10*pi*t)
0.4
0.6
0.8
1
1xa3
-1-1
-0.8
-0.6
-0.4
-0.2
0t
0.2
0.4
0.6
0.8
1
图1 连续信号
xa1(t)=cos(2*pi*t)
xa1
t
xa2(t)=-cos(6*pi*t)
xa2
t
xa3(t)=cos(10*pi*t)
xa3
t
图2 对连续信号进行采样