Question

Answer 1

\(A_n^3+C_n^{n-2}=14n\Rightarrow n=5\)

Xét khai triển: 

\(\left(x-1\right)^{25}=\sum\limits^{25}_{k=0}C_{25}^k.x^k.\left(-1\right)^{25-k}\)

Do \(x^{10}=x^9.x^1=x^8.x^2=x^7.x^3=...=1.x^{10}\) nên:

Hệ số chứa \(x^{10}\) là:

\(\sum\limits^{10}_{k=1}C_{25}^k.\left(-1\right)^{25-k}=-1961255\)