Hey, I'm going over series expansions and was wondering if someone could check my work and tell me if my work is correct. If not, could you explain it to me? I couldn't find any example like this problem in my book so I'm posting it online. Here it is, The closed form series expansion for cos(x) is Ʃ[(-1)^n(x)^2n]/(2n)!. Use this series to find a series expression for [cos(x)-1]/x^2. Okay here's what I did: [cos(x)-cos(pi)]/(x)^(2) (x)^(-2)*Ʃ[(-1)^(n)(x)^(2n)-(pi)^(2n)]/(2n)! Ʃ[(-1)^(n)(x)^(2n-2)-(pi)^(2n) Is that the way I'm supposed to do it? Thanks!