a) $\sqrt[4]{x-\sqrt{x^{2}-1}}+\sqrt{x+\sqrt{x^{2}-1}}=2$
$\frac{\sqrt[4]{(x+\sqrt{x^{2}-1})(x-\sqrt{x^{2}-1)}}{\sqrt[4]{x+\sqrt{x^{2}+1}}}+\sqrt{x+\sqrt{x^{2}+1}}=2$
<=> $\frac{1}{\sqrt[4]{x+\sqrt{x^{2}+1}}}+\sqrt{x+\sqrt{x^{2}+1}}=2$
Đặt $\frac{1}{\sqrt[4]{x+\sqrt{x^{2}+1}}}=a$
<=> $a^{2}+\frac{1}{a}=2$
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