Hi,

I searched how to compute this serie.
Can you tell if the steps below are correct?
S1=1+1+1+1+...
S2=1-1+1-1+...=1/2
So
S1+S2=1+2+0+2+0+...
S1+S2-1=2+0+2+0+...
=2*S1
S1+1/2-1=2*S1
S1=-1/2