can giup do

D

dien0709

[TEX](x^2+1)^n=a_nx^{2n}+a_{n-1}x^{2n-2}+...+a_1x^2+1[/TEX]
[TEX]x=1\Rightarrow 2^n=a_n+a_{n-1}+...+a_1+1=1024=2^{10}\Rightarrow n=10[/TEX]
[TEX]C^k_{10}(x^2)^k=ax^{12}\Rightarrow k=6\Rightarrow a=C^6_{10}=210[/TEX]
 
H

halancute

hoi them

cho minh` hoi may cai chu: a(n), a(n-1), a(n-2)..con` chu C dau. kho hieu cho do nhat
a: la ki hieu gi` vay?
co phai la` ntn ko : a(n)=chinh hop chap 0 cua n p.tu
a(n-1)=------------------1-------------
a(n-2)=------------------2-------------
 
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