Ta có: \(\left(1+\frac{1}{x}\right)^3\left(1+x\right)^3=16\)
\(\Leftrightarrow\left[\left(1+\frac{1}{x}\right)\left(1+x\right)\right]^3=16\)
\(\Leftrightarrow\left(\frac{\left(x+1\right)^2}{3}\right)^3=16\)
\(\Leftrightarrow\frac{\left(x+1\right)^6}{27}=16\)
\(\Leftrightarrow\left(x+1\right)^6=432\)
Đến đây bí rồi