VD5:
\(A\cap B\ne\varnothing\Leftrightarrow2m-1\le m+3\)
\(\Leftrightarrow m\le4\)
VD6:
\(A\cap B\ne\varnothing\Leftrightarrow9a>\dfrac{4}{a}\)
\(\Leftrightarrow\dfrac{9a^2-4}{a}>0\)
\(\Leftrightarrow9a^2-4< 0\) (do \(a< 0\))
\(\Rightarrow-\dfrac{2}{3}< a< \dfrac{2}{3}\)
\(\Rightarrow-\dfrac{2}{3}< a< 0\)
VD6:
\(A\cap B=A\Leftrightarrow A\subset B\)
\(\Leftrightarrow\left\{{}\begin{matrix}-1\ge m\\3\le m+5\end{matrix}\right.\) \(\Rightarrow-2\le m\le-1\)
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