即将离开知乎
您即将离开知乎,请注意您的账号和财产安全。
https://math.stackexchange.com/questions/2050657/why-are-sine-and-cosine-called-harmonic-functions
您即将离开知乎,请注意您的账号和财产安全。
https://math.stackexchange.com/questions/2050657/why-are-sine-and-cosine-called-harmonic-functions