18.Tự tìm ĐKXĐ nhé
\(A=\left(\dfrac{a\sqrt{a}-1}{a-\sqrt{a}}-\dfrac{a\sqrt{a}+1}{a+\sqrt{a}}\right):\dfrac{a+2}{a-2}\)
\(A=\left(\dfrac{\sqrt{a^3}-1^3}{\sqrt{a}\left(\sqrt{a}-1\right)}-\dfrac{\sqrt{a^3}+1}{\sqrt{a}\left(\sqrt{a}+1\right)}\right).\dfrac{a-2}{a+2}\)
\(A=\left(\dfrac{\left(\sqrt{a}-1\right)\left(a+\sqrt{a}+1\right)}{\sqrt{a}\left(\sqrt{a}-1\right)}-\dfrac{\left(\sqrt{a}+1\right)\left(a-\sqrt{a}+1\right)}{\sqrt{a}\left(\sqrt{a}+1\right)}\right).\dfrac{a-2}{a+2}\)
\(A=\left(\dfrac{a+\sqrt{a}+1}{\sqrt{a}}-\dfrac{a-\sqrt{a}+1}{\sqrt{a}}\right).\dfrac{a-2}{a+2}\)
\(A=\dfrac{a+\sqrt{a}+1-a+\sqrt{a}-1}{\sqrt{a}}.\dfrac{a-2}{a+2}\)
\(A=\dfrac{2\sqrt{a}}{\sqrt{a}}.\dfrac{a-2}{a+2}\)
\(A=\dfrac{2\left(a-2\right)}{a+2}\)