\(=\sqrt{\dfrac{a-1}{a+2}:\dfrac{a+2}{\left(a-1\right)^3}}\)
\(=\sqrt{\dfrac{\left(a-1\right)^4}{\left(a+2\right)^2}}=\dfrac{\left(a-1\right)^2}{a+2}\)
Với a > 1
\(\sqrt{\dfrac{a-1}{a+2}}:\sqrt{\dfrac{a+2}{\left(a-1\right)^3}}=\dfrac{\sqrt{a-1}\left(a-1\right)\sqrt{a-1}}{a+2}=\dfrac{\left(a-1\right)^2}{a+2}\)