Question

Answer 1

a) D có nghĩa <=> các phân số trong D có nghĩa 
\(< =>3+\sqrt{a}\ne0;9-a\ne0;a-3\sqrt{a}\ne0;\sqrt{a}\ne0;a\ge0\)
\(< =>\sqrt{a}\ne-\sqrt{3};a\ne9;\left\{{}\begin{matrix}a\ne0\\a\ne9\end{matrix}\right.;a\ne0;a\ge0\)
\(< =>\left\{{}\begin{matrix}a\ne9\\a>0\end{matrix}\right.< =.0< a\ne9\)
b) \(=\dfrac{3\sqrt{a}-a+a+9}{\left(\sqrt{a}+3\right)\left(3-\sqrt{a}\right)}:\dfrac{3\sqrt{a}+1-\sqrt{a}+3}{\sqrt{a}\left(\sqrt{a}-3\right)}=\dfrac{-3\sqrt{a}}{2\sqrt{a}+4}\)