**Parseval's theorem**
[Conservation of Energy](https://texonom.com/conservation-of-energy-d38bcc0c84854c998af26eae9b775503) 


### The average power is the sum of average powers in all harmonics
So [Trivial](https://texonom.com/trivial-2d7ac81afb304cedac671daa7dcba202) 



### [DTFS](https://texonom.com/dtfs-924b5dfa43dd46638de66cc15f61b538) 
$$\frac{1}{N}\sum|x[n]|^2 = \sum|a_k|^2$$



> [Parseval's theorem](https://en.wikipedia.org/wiki/Parseval's_theorem)





