Chuỗi Fourierf(x)=a02+∑n=1∞(ancosnx+bnsinnx)f(x) = \frac{a_0}{2} + \sum_{n=1}^{\infty}(a_n\cos nx + b_n\sin nx)f(x)=2a0+n=1∑∞(ancosnx+bnsinnx)Hệ sốan=1π∫−ππf(x)cos(nx) dxa_n = \frac{1}{\pi}\int_{-\pi}^{\pi}f(x)\cos(nx)\,dxan=π1∫−ππf(x)cos(nx)dxbn=1π∫−ππf(x)sin(nx) dxb_n = \frac{1}{\pi}\int_{-\pi}^{\pi}f(x)\sin(nx)\,dxbn=π1∫−ππf(x)sin(nx)dxSóng vuôngf(x)=4π∑k=1∞sin((2k−1)x)2k−1f(x) = \frac{4}{\pi}\sum_{k=1}^{\infty}\frac{\sin((2k-1)x)}{2k-1}f(x)=π4k=1∑∞2k−1sin((2k−1)x)👉 Khai triển trên AhaStep