Đặt

Câu hỏi: Đặt $f\left(n\right)={(n2+n+1)}^2+1.$ Xét dãy số $\left(u_n\right)$ sao cho $u_n=\frac{f\left(1\right).f\left(3\right).f\left(5\right)...f(2n-1)}{f\left(2\right).f\left(4\right).f\left(6\right)...f\left(2n\right)}$. Tính lim n$\sqrt{u_n}$

A.$lim n\sqrt{u_n}=\sqrt{2}$

B.$lim n\sqrt{u_n}=\frac{1}{\sqrt{3}}$

C.$lim n\sqrt{u_n}=\sqrt{3}$

D.$lim n\sqrt{u_n}=\frac{1}{\sqrt{2}}$