§4. Các tập hợp số

\(A\cap B\ne\varnothing\Rightarrow\left\{{}\begin{matrix}m\le1\\3m+2\ge-2\end{matrix}\right.\)

\(\Rightarrow-\dfrac{4}{3}\le m\le1\)

\(X=\left\{-1;1\right\};\left\{-2;-1;1\right\};\left\{-1;1;2\right\};\left\{-2;-1;1;2\right\}\)

\(A\cap B\ne\varnothing\Rightarrow\left\{{}\begin{matrix}m\le1\\3m-2\ge-2\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}m\le1\\m\ge0\end{matrix}\right.\)

\(\Rightarrow0\le m\le1\)

\(A\cup B=\left(-\infty;-2\right)\cup\left(0;+\infty\right)\)

\(\Rightarrow\left(A\cup B\right)\cap C=\left(-3;-2\right)\cup\left(0;2\right)\)

Có n phần tử

c: \(A=(2;9]\)

B=(3;5]

\(A\cap B=\)=(3;5]

\(A\cup B=\)(2;9]

A\B=(2;3]

B\A=\(\varnothing\)

10.C

11.A

12.D

\(\left(2x+x^2\right)\left(x^2-3x+2\right)=0\Leftrightarrow x\left(x+2\right)\left(x-1\right)\left(x-2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=0\\x=-2\\x=1\\x=2\end{matrix}\right.\\ A=\left\{-2;0;1;2\right\}\)

\(3\le x^3\le27\Leftrightarrow x\in\left\{2;3\right\}\\ B=\left\{2;3\right\}\)

\(\Leftrightarrow A\cup B=\left\{-2;0;1;2;3\right\}\)

Bài 6:

ĐK: \(9a< \dfrac{4}{a}\Leftrightarrow a^2< \dfrac{4}{9}\Leftrightarrow-\dfrac{2}{3}< a< \dfrac{2}{3}\)

Bài 7:

ĐK: \(a=\dfrac{4}{a}\Leftrightarrow a^2=4\Leftrightarrow\left[{}\begin{matrix}a=2\\a=-2\end{matrix}\right.\)