b,

\(\sqrt{9-4\sqrt{5}}-\sqrt{5}\)

\(=\sqrt{4-2.2\sqrt{5}+5}-\sqrt{5}\)

\(=\sqrt{\left(2-\sqrt{5}\right)^2}-\sqrt{5}\)

\(=\left|2-\sqrt{5}\right|-\sqrt{5}\)

\(=\sqrt{5}-2-\sqrt{5}=-2\) ( 2 < \(\sqrt{5}\))

mấy bác tranh câu a e làm câu b

\(\dfrac{x-3}{x-4}< 0\)

-3 > - 4 =>

\(\Leftrightarrow\left\{{}\begin{matrix}x-3>0\\x-4< 0\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x>3\\x< 4\end{matrix}\right.\)

=> 3 < x < 4

b,

\(\dfrac{x-1}{x+3}>0\)

-1 < 3

\(\Leftrightarrow\left[{}\begin{matrix}x-1>0\\x+3< 0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x>1\\x< -3\end{matrix}\right.\)

=> ...

=== không quen dùng bảng xét dấu