# Re-writting an Equation

1. Jul 16, 2009

### S_David

1. The problem statement, all variables and given/known data

Hello,

I have the following equation:

$$f(x)=\sum_{r=m}^{M_B}\,\sum_{i=0}^{M_B-r}\,\sum_{j=0}^{r+i}\,\sum_{k=0}^{j(N_B-1)}(-1)^{i+j}{M_B\choose r}{M_B-r\choose i}{r+i\choose j}\left(\frac{x}{C}\right)^k\,e^{jx/C}$$

and I want to write it in the form of $$f(x)=1+R(x)$$

2. Relevant equations

$$m$$ will be any number from 1 up to $$M_B$$, and $$f(x)=1-e^{x/C}$$ for $$M_B=N_B=1$$.

3. The attempt at a solution

I tried to extract the following parameters to have the 1 value:

$$r=M_B, i=0, j=0, k=0$$

but after that I don't know what to do by the indices. It does not seem straightforward as one can see.

Regards