For each of these generating functions, provide a closed formula for the sequence it determines.

a) (x^2 + 1)^3

b) (3x - 1)3 c) 1/(1 - 2x^2)

d) x^2/(1 - x)^3 e) x-1+(1/(1-3x))

f) (1+x^3)/(1+x)^3

g) x/(1+x+x^2)