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**shotgun1** Hi all,

Would really appreciate if someone could assist me on the following please: Casella and berger provide an example on pg 329 where they state:

$\displaystyle $-t_1+\log t_1\sum_{x_1=0}^{\infty}x_1\frac{e^{-t_1^{(r)}}(t_1^{(r)})^{x_1}}{x_1!}= -t_1 +t_1^{(r)}\log t_1$$

I was having problems seeing how $\displaystyle $\sum_{x_1=0}^{\infty}x_1\frac{e^{-t_1^{(r)}}(t_1^{(r)})^{x_1}}{x_1!}$$ can therefore equal $\displaystyle $t_1^{(r)}$$. Please could someone help, thanks!!