You need to mess around with the series for the Bessel function of the first kind:
Clearly,
Now, make a substitution. Let . Then,
A couple observations need to be made to finish it up.
Can you proceed?
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yes I think I got it ( thank you very very mach )
because the Gamma function of the negative integer = infinity
so the first part = zero
and the 2.nd part ( will be ) = (-1)^n Jn(x) ( but need some work )