# A Differentiation and Summation

1. Dec 27, 2016

### mahmud_dbm

Dear Friends

So, i have this special case where i have to do a differentiation and summation.

Is it okay ?? Or, i how should i proceed with this ?

2. Dec 28, 2016

### Ssnow

ok, what you did in the bracket were algebraic operations and the use of the formula for geometric series $\sum_{k=0}^{N-1}t^{k}=\frac{t^{N}-1}{t-1}$ where $k=e^{-j\pi(2n/N-1)}$, now you must derive the expression respect $\chi$ ...