第2章 2.17

(1)

$\frac{1}{\sqrt{x}-\sqrt{x-2}} = \frac{\sqrt{x}+\sqrt{x-2}}{x-(x-2)} = \frac{\sqrt{x}+\sqrt{x-2}}{2}$

(2)

$\frac{2}{\sqrt{1+2a}+\sqrt{1-2a}} = \frac{2\left(\sqrt{1+2a}-\sqrt{1-2a}\right)}{(1+2a)-(1-2a)} = \frac{\sqrt{1+2a}-\sqrt{1-2a}}{2a}$

$a = 0$ のとき分母が $0$ となり成り立たない

$a = 0$ のとき $\dfrac{2}{\sqrt{1}+\sqrt{1}} = 1$