Fourier expand

例句：

1. 1.The Fourier transform is a powerful tool for analyzing signals.
   傅里叶变换是分析信号的一种强大工具。
2. 2. In Fourier analysis, the signal is expanded into its constituent frequencies.
   在傅里叶分析中，信号被扩展到其构成的频率上。
3. 3.The Fourier expansion of a function provides insight into its behavior.
   函数的傅里叶展开提供了对其行为的见解。