Thread: To sum n terms

Hi,

iS THERE Any one out there who can provide an expression for the sum of n terms:

i*X* COS i*X

where X is in radians, and i varies from 1 to n?

Thanks in advance for your help.

Cheers

Dear Almo,

you can put out the x front of a bracket, I mean:
sum i*x*cos(i*x) = x*sum i*cos(i*x)

It can be interesting eventuell the derivation of sin(i*x) is.

Originally Posted by Almo

Hi,

iS THERE Any one out there who can provide an expression for the sum of n terms:

i*X* COS i*X

where X is in radians, and i varies from 1 to n?

Thanks in advance for your help.

Cheers

I take it that in this case is your counter, not the imaginary number ?


So you're asking what does

equal right?

G'day


Many thanks for your interest.

Yes you are correct that i is NOT an imaginary number i.e. sqrt(-1).

It is as you say the sum of the terms whereby i is initialy 1 then increases by 1 to the limit n.

How about this use the following lemma



So your sum of and apply the above lemma with

Thanks for your suggestion. I'm afraid I don't understand if your last line is my desired answer. Would you please rephrase your solution in terms of my i and X?

Cheers