Thu gọn \(\mathrm{B}=\sqrt[...

D

- Hướng dẫn giải

\(\begin{array}{l} \text { Đặt } x_{0}=\sqrt[3]{70-\sqrt{4901}}+\sqrt[3]{70+\sqrt{4901}} \\ \Rightarrow x_{0}^{3}=\left(\sqrt[3]{70-\sqrt{4901}+\sqrt[3]{70+\sqrt{4901}})^{3}}\right. \\ =70-\sqrt{4901}+70+\sqrt{4901}+3 \sqrt[3]{70-\sqrt{4901}} \sqrt[3]{70+\sqrt{4901}}(\sqrt[3]{70-\sqrt{4901}}+\sqrt[3]{70+\sqrt{4901}}) \\ =140+3 x \end{array}\)

Khi đó ta có

\(\begin{array}{l} x_{0}^{3}+3 x_{0}-140=0 \Leftrightarrow\left(x_{0}-5\right)\left(x^{2}+5 x+28\right)=0 \\ \text { Mà } x_{0}^{2}+5 x_{0}+28>0(\text { do } \Delta<0) \Rightarrow x_{0}=5 \\ \text { Vậy } B=5 \end{array}\)