- #1
athrun200
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Homework Statement
Show that
[itex]\cos x[/itex]=[itex]J_{0}[/itex]+[itex]2[/itex][itex]\sum(-1)^{n}[/itex][itex]J_{2n}[/itex]
where the summation range from n=1 to +inf
Homework Equations
Taylor series for cosine?
series expression for bessel function?
The Attempt at a Solution
My approach is to start from R.H.S.
I would like to express all bessel functions in the series form, then compare it to the taylor series of cosine.
I notice that the summation can be written as
-[itex]J_{2}[/itex]+[itex]J_{4}[/itex]-[itex]J_{6}[/itex]+[itex]J_{8}[/itex]+...
Using the recurrence relation, we have - [itex]2J'_{3}[/itex]-[itex]2J_{7}[/itex]-[itex]2J_{11}[/itex]-...
Therefore, R.H.S can be written as[itex]J_{0}+[/itex] [itex]4J'_{3}[/itex]-[itex]4J_{7}[/itex]-[itex]4J_{11}[/itex]-...
But it seems it will be extremely difficult to deal with it. Since each term itself is a series. We are now summing up infinity many series.
I wonder if we have a better way to finish this question