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# sum of complex exponentials result-zero/non-zero watch

1. Hi,

This is probably a stupid question, I understand that it is equal to p if p divides n.
But I don't understand why it is zero otherwise.

For example if I have n/p=1/2
then

E.g also say p=5 then I have

i gues im doing something stupid?

ta.
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2. (Original post by nologiceretoday)
Hi,

This is probably a stupid question, I understand that it is equal to p if p divides n.
But I don't understand why it is zero otherwise.

For example if I have n/p=1/2
then

E.g also say p=5 then I have

i gues im doing something stupid?

ta.
It is a geometric series so just use the formula and the result just falls out.
3. (Original post by nologiceretoday)
Hi,

This is probably a stupid question, I understand that it is equal to p if p divides n.
But I don't understand why it is zero otherwise.

For example if I have n/p=1/2
then

E.g also say p=5 then I have

i gues im doing something stupid?

ta.
If n/p is 1/2, and p is also 5, then n = 2.5, and isn't an integer.

B_9710's post covers the part about equalling zero.
See DFranklin, below
4. (Original post by B_9710)
It is a geometric series so just use the formula and the result just falls out.
by the numerator. Now if I am to consider the case that p divides n, and rename this integer as m I have how would I evaluate this to p?
5. (Original post by nologiceretoday)
by the numerator. Now if I am to consider the case that p divides n, and rename this integer as m I have how would I evaluate this to p?
Note that the standard formula for the sum of a GP is not valid when the common ratio is 1. On the other hand, it is not hard to find the sum of a series of p terms that are all the same.

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