- $\sum_{k=0}^{n}\sin{(x+ky)}=\frac{\sin{\frac{(n+1)y}{2}}\sin{\left(x+\frac{ny}{2} \right)}}{\sin{\frac{y}{2}}}$.
- $\sum_{k=0}^{n}\cos{(x+ky)}=\frac{\sin{\frac{(n+1)y}{2}}\cos{\left(x+\frac{ny}{2} \right)}}{\sin{\frac{y}{2}}}$.
- $\sum_{k=1}^{n}\sin{kx}=\frac{\sin{\frac{nx}{2}}\sin{\frac{(n+1)x}{2}}}{\sin{\frac{x}{2}}}$.
- $\sum_{k=1}^{n}\cos{kx}=\frac{\sin{\frac{nx}{2}}\cos{\frac{(n+1)x}{2}}}{\sin{\frac{x}{2}}}$.
Bài viết đã được chỉnh sửa nội dung bởi dark templar: 08-09-2012 - 20:25