1 chứng minh các đẳng thức sau
a, \(\dfrac{a+b}{b^2}\sqrt{\dfrac{a^2b^4}{a^22ab+b^2}}=\left|a\right|\)
b, \(\dfrac{a\sqrt{b}+b\sqrt{a}}{\sqrt{ab}}:\dfrac{a}{\sqrt{a}-\sqrt{b}}=a-b\)
c,\(\left(\dfrac{\sqrt{x}+\sqrt{y}}{\sqrt{x}-\sqrt{y}}-\dfrac{\sqrt{x}-\sqrt{y}}{\sqrt{x}+\sqrt{y}}\right):\dfrac{\sqrt{xy}}{x-y}=4\)
a) Sai đề.
\(\dfrac{a+b}{b^2}\sqrt[]{\dfrac{a^2b^4}{a^2+2ab+b^2}}=\dfrac{a+b}{b^2}.\dfrac{b^2\left|a\right|}{\left|a+b\right|}=\left|a\right|\)
b) Sai đề.
\(\dfrac{a\sqrt[]{b}+b\sqrt[]{a}}{\sqrt[]{ab}}:\dfrac{1}{\sqrt[]{a}-\sqrt[]{b}}=\dfrac{\sqrt[]{ab}\left(\sqrt[]{a}+\sqrt[]{b}\right)}{\sqrt[]{ab}}.\left(\sqrt[]{a}-\sqrt[]{b}\right)=a-b\)
c) \(\left(\dfrac{\sqrt{x}+\sqrt[]{y}}{\sqrt[]{x}-\sqrt[]{y}}-\dfrac{\sqrt[]{x}-\sqrt[]{y}}{\sqrt[]{x}+\sqrt[]{y}}\right):\dfrac{\sqrt[]{xy}}{x-y}\)
\(=\dfrac{\left(\sqrt[]{x}+\sqrt[]{y}\right)^2-\left(\sqrt[]{x}-\sqrt[]{y}\right)^2}{\left(\sqrt[]{x}-\sqrt[]{y}\right)\left(\sqrt[]{x}+\sqrt[]{y}\right)}.\dfrac{x-y}{\sqrt[]{xy}}=\dfrac{4\sqrt[]{xy}}{x-y}.\dfrac{x-y}{\sqrt[]{xy}}=4\)
