Help w/ Geometric Series Involving cos(xn)

[yellowjack]

I need to show that:

2*sum[ (( 1/3)^t) * cos(wt) ]
where we are summing from t=1 to inf, is equal to:
( 1 - 3cos(w) ) / ( 3cos(w) - 5 )

Any links/tips would be helpful. I haven't been able to find anything via google.

[ADDboy]

cos(wt) is the real part of exp(iwt), so your series is the real part of an absolutely convergent complex geometric series.

[yellowjack]

ok
solved in probability forum
thanks for the post ADDboy