Question

Answer 1

Thay \(x=y=1\) ta được:

\(\left(1+2\right)^{10}=C_{10}^0+2.C_{10}^1+2^2.C_{10}^2+...+2^{10}.C_{10}^{10}\)

\(\Rightarrow3^{10}=1+2.C_{10}^1+2^2.C_{10}^2+...+2^{10}.C_{10}^{10}\)

\(\Rightarrow\dfrac{1}{2}\left(3^{10}-1\right)=C_{10}^1+2.C_{10}^2+...+2^9.C_{10}^{10}\)

Đáp án B