求 a^n-b^n的展開式.

an - bn =
圖片參考：http://www.futura-sciences.com/cgi-bin/mimetex.cgi?(a-b)%20\displaystyle\sum_{k=0}^n%20a^{n-k}b^k

this???

http://en.wikipedia.org/wiki/Factorization

你是指 factorized form，是嗎？an – bn ≡ (a – b) (an–1 + an–2 b + an–3 b2 + … + a bn–2 + bn–1)

a^n － b^n
＝ (a－b) [a^(n-1) + a^(n-2)b + a^(n-3)b^2 + .....................+ ab^(n-2) + b^(n-1)]