实现f(x)以及N=1,2,5,7时，傅里叶级数的部分和SN(x)的图像。观察部分和SN的图像与f图像的接近情况。对区间-2π≤x≤2π重复以上过程。(F (x) and N=1,2,5,7, the part of Fourier series and the image of SN (x). The image of the observation part and the SN is close to the f image. The interval -2 = x = 2 pi pi repeat.)