b]1. The problem statement, all variables and given/known data[/b] prove that [tex]\sum[/tex]( (e^(-u)) (u(^(x)) )/x! (from x=o to n ) = [tex]\int[/tex] ( (e^(-y))(y^n) )dy/n! (from u to infinite ) 2. Relevant equations 3. The attempt at a solution i know that the left is Poisson distribution formular but how to do with the 'sum' ? and the right one i got a infinite series , use integration by part .but i don not know how to simplicity it . is there anything else i can use for this question ?