Câu hỏi: a-(5 căn a)+6 =0 tìm a

`a-5\sqrt{a} + 6=0` ( ĐKXĐ a≥0 )

`<=> a- 2\sqrt{a}-3\sqrt{a}+6=0`

`<=> \sqrt{a}(\sqrt{a}- 2)-3(\sqrt{a}-2)=0`

`<=> (\sqrt{a} - 2)(\sqrt{a}-3)=0`

`<=>`\(\left[ \begin{array}{l}\sqrt{a}-2=0\\\sqrt{a}-3=0\end{array} \right.\)

`<=>` \(\left[ \begin{array}{l}\sqrt{a}=2\\\sqrt{a}=3\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}a=4\\a=9\end{array} \right.\) 

Vậy `a ∈ {4;9}`