I am given a coefficient to estimate as a assignment question. But I am unable to think how it must be true.

**Notations** Let $l$ belongs to $\{1, 2,\ldots,a\}$ and $j$ belongs to $\{0,1,\ldots,n\}$. Assume that this equation holds

$$

c_{l,j,n}=\frac{1}{2\pi i}\int_{|z+j+1|=\frac{1}{2}} R_n(t) (z+j+1)^{l-1}\mathrm{d}z.

$$

where

$$

R_n(t) = \frac{(n!)^{a-2r} ×(t-rn+1)_{rn} (t+n+2)_{rn}}{(t+1)_{n+1}}.

$$

Also note that

$$

D_{\lambda}=\frac{1}{\lambda! }\times\frac{d^{\lambda}}{dt^{\lambda}}

$$

and

$$

c_{l,j,n}=D_{a-l}(R_n(t)(t+j+1)^a)_{t=-j-1}.

$$

These identities are to be used but have already been proved by me.

$$

\begin{split}

|(z-rn+1)_{rn}|&\leq (j+2)_{rn}\\

|(z+n+2) _{rn}|&\leq (n-j+2)_{rn}\\

|(z+1)_{n+1}|&\geq 2^{-3} (j-1)! (n-j-1)!

\end{split}

$$

Now, I am unable to think how to deduce next step which is (adding it’s image) ->

I don’t know how to deduce this from (1) and related results given and how did integral just vanished?