Hi

I am given that:

P(Y=k)= p^k.(1-p)^(n-k).e^-x.(x^n/n!)

where the sum is from n=k to infinity

and I need to show that Y is poission distributued with parameter p

I'm not really sure where to start, should I take out all the variables which are not raised to the power of n out of the sum and change to n!/(n-k)!k!?

Any tips to get me started would be much appreciated