Hi. I saw that there were a pair of threads that discussed these series but since it was far away from my knowledge I decided to start my own. I have just been introduced to these series and found out that the series on the form of: a_0 + a_1*x + a_2*x^2 + a_3*x^3 + .... Where a_0 = 1 a_1 = 0 a_2 = 1 a_3 = 0 a_4 = 1 ... Can be descirbed with the equation (1-x^2)^-1 as long as -1 ≤ x ≤ 1, i.e. it is convergence. But I also read that even though the answers where x is either smallar than -1 or bigger than 1 seems like nonsens, this isnt the case. For example when x = 2 the author writes That the equation,(1-x^2)^-1, gives. Now in which way can -1/3 make any meaning when the series clearly goes to infinity?