nhị thức niu ton

H

hthtb22

Hướng dẫn
Xét đa thức $f(x)=(1+x)^n $
$f'(x)=n(1+x)^{n-1}$
$f"(x)=n(n-1)(1+x)^{n-2})$

$f"(1)=n(n-1).2^{n-2}$

$f(x)=C^0_n+C^1_n.x+\sum_{k=2}^{n} C^k_n.x^k$
$f'(x)=C^1_n+\sum_{k=2}^{n} k.C^k_n.x^{k-1}$
$f(x)=\sum_{k=2}^{n} k(k-1)C^k_n.x^{k-2}$

Cho $x=1$
 
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