method 2

           1
f(x) = --------- = (1-x)^-2 =
        (1-x)^2

 -2  -2    0     -2  -3    1     -2  -4    2
C  (1) (-X)  +  C  (1) (-X)  +  C  (1) (-X)  +  ... =
  0               1               2

1 + 2x + 3x^2 + ... =

 ∞
 Σ (n+1)x^n
n=0         #

※ 編輯: flyfound        來自: 218.166.206.14       (07/04 00:56)