I am trying to evaluate the following summation:

Please look at page 3 in the book link

Adventures in stochastic Processes, page 3

When he is deriving the expectation of a geometric random variables variable he writes E(X) as a double summation and then changes the order of summation. My doubt is when can you and when can you not reverse the order of summations and HOW DO YOU DETERMINE the limits of summation when you change the order of summation

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I did not understand how the limits of the indices j and k change when you reverse the order of summations..please help

I am trying to evaluate the following summation:

Please look at page 3 in the book link

Adventures in stochastic Processes, page 3

When he is deriving the expectation of a geometric random variables he writes E(X) as a double summation and then changes the order of summation. My doubt is when can u you and when can u you not reverse the order of summations and HOW DO U YOU DETERMINE the limits of summation when u you change the order of summation

i did not understand how the limits of the indices j and k change when u you reverse the order of summations..plz summations..please help

I am trying to evaluate the following summation:

Please look at page 3 in the book link

Adventures in stochastic Processes, page 3

When he is deriving the expectation of a geometric random variables he writes E(X) as a double summation and then changes the order of summation. My doubt is when can u and when can u not reverse the order of summations and HOW DO U DETERMINE the limits of summation when u change the order of summation

i did not understand how the limits of the indices j and k change when u reverse the order of summations..plz help