→ yes987789 :謝謝! 那sigma C(n,i)*i*(1-x)^i*x^(n-i)能化簡嗎 06/05 10:11
n
Σ C(n,k) k [(1 - x)^k][x^(n - k)]
k=0
d
= (1 - x )x^(n - 1) ---------- Σ C(n,k) [1/x - 1]^k
d[1/x - 1]
= (1 - x)x^(n - 1) n x^(- n + 1)
= n - nx
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