Sử dụng ký hiệu khoảng để viết tập hợp sau đây: $E = \left( {4; + \infty } \right)\backslash \left( {-\infty ;2} \right]$.

\(\emptyset \)

\(\left[ {0;5} \right]\)

\(\left[ {3;4} \right]\)

\(\left\{ {3;4} \right\}\)

$a > 0,\,\,b < 0,\,\,c > 0$

$a < 0,\,\,b > 0,\,\,c > 0$

$a < 0,\,\,b < 0,\,\,\,c < 0$

$a < 0,\,\,b < 0,\,\,c > 0$

$2\overrightarrow {GM} $.

$\dfrac{2}{3}\overrightarrow {GM} $.

$ - \dfrac{2}{3}\overrightarrow {AM} $.

$\dfrac{1}{2}\overrightarrow {AM} $.

\(y =  - {\left( {x + 1} \right)^2}\).

\(y =  - {\left( {x - 1} \right)^2}\).

\(y = {\left( {x + 1} \right)^2}\).

\(y = {\left( {x - 1} \right)^2}\).

\(\left( {0;3} \right)\). 

\(\left( {\dfrac{1}{3};0} \right)\).

\(\left( {0;2} \right)\).

\(\left( {4;2} \right)\).

$a$.    

$\sqrt 2 a$.

$\dfrac{a}{2}$.

$2a$.

$\{ 3;5\} $

$\{ 1;{\rm{ }}3;{\rm{ }}5;{\rm{ }}7;{\rm{ }}8;{\rm{ }}9\} $ .

$\{ 1;{\rm{ }}7;{\rm{ }}9\} .$          

$\{ 1;{\rm{ }}3;{\rm{ }}5\} .$