- #1
Dustinsfl
- 2,281
- 5
$$
g'(\theta) = 2\sum_{n = 1}^{\infty}(-1)^{n + 1}\cos n\theta.
$$
How can I show that this series diverges for all values other than $\pm\frac{\pi}{2}$?
g'(\theta) = 2\sum_{n = 1}^{\infty}(-1)^{n + 1}\cos n\theta.
$$
How can I show that this series diverges for all values other than $\pm\frac{\pi}{2}$?