>>439
f(x)=1/{(1-x)(2+3x) } = (1/5) {1/(1-x)} + (1/5){ 3/(2+3x)}
で

1/(1-x) = Σx^k
だから
3/(2+3x) = 1/(1+(3/2)x) = Σ (-(3/2)x)^k