Câu hỏi 27
Nếu $$
\begin{aligned} x+\sqrt{x^2-1} &+\frac1{x-\sqrt{x^2-1}}\\ &=20, \end{aligned}
$$ thì $$
\begin{aligned} x^2+\sqrt{x^4-1} &+\frac1{x^2+\sqrt{x^4-1}}\\ &= \end{aligned}
$$
\begin{aligned} x+\sqrt{x^2-1} &+\frac1{x-\sqrt{x^2-1}}\\ &=20, \end{aligned}
$$ thì $$
\begin{aligned} x^2+\sqrt{x^4-1} &+\frac1{x^2+\sqrt{x^4-1}}\\ &= \end{aligned}
$$