3)
a) Điều kiện: $
\left\{\begin{matrix}
\sqrt{x} + \sqrt{y} \neq 0 \\ \sqrt{x} - \sqrt{y} \neq 0
\end{matrix}\right.
\Leftrightarrow
\left\{\begin{matrix}
x>0 \\ y>0
\end{matrix}\right.
$
b) $A= \dfrac{ (\sqrt{x}-\sqrt{y})^2+4 \sqrt{xy}}{\sqrt{x} + \sqrt{y}} - \dfrac{x-y}{\sqrt{x} - \sqrt{y}} \\
= \dfrac{x-2 \sqrt{xy}+y+4 \sqrt{xy}}{ \sqrt{x} + \sqrt{y}} - \dfrac{(\sqrt{x} - \sqrt{y})(\sqrt{x} + \sqrt{y})}{\sqrt{x} - \sqrt{y}} \\
= \dfrac{x+2 \sqrt{xy}+y}{\sqrt{x} + \sqrt{y}} - (\sqrt{x} + \sqrt{y}) \\
= \dfrac{(\sqrt{x} + \sqrt{y})^2}{\sqrt{x} + \sqrt{y}} - \sqrt{x} - \sqrt{y} \\
= \sqrt{x} + \sqrt{y} - \sqrt{x} - \sqrt{y} = 0$
[TẶNG BẠN] TRỌN BỘ Bí kíp học tốt 08 môn
