添加常量并调整频率:

x = 5 + 15*sin(2*pi*t/24);

在您的代码中，频率不正确，并且采样周期对于该频率而言太大:您有混叠.这就是为什么看不到正弦波的原因.

In your code the frequency is incorrect, and the sampling period is too large for that frequency: you have aliasing. That's why you don't see a sine wave.