Let the G.P. be : a , ar , ar2 , ar3 , ............ ar2n - 1 where 'r' is the common ratio
Given : S1 = a + ar2 + ar4 + ........... + ar2n - 2 = a( (r2 )n - 1 ) / r2 - 1
S2 = ar + ar3 + ar5 + ............. + ar2n - 1 = ar ( (r2)n - 1 ) / r2 - 1
Therefore : S2 / S1 = r