A.\(\dfrac{1}{2}\)
B.\( - \dfrac{1}{2}\)
C.\( - 3\)
D.\(3\)

A.\(4\)
B.\(2\)
C.\(2\sqrt 6 \)
D.\( - 2\)

A.\(D\left( { - 1;1} \right)\) và \(C\left( { - 2;4} \right)\)
B.\(A\left( {1;1} \right)\) và \(B\left( {2;4} \right)\)
C.\(A\left( {1;1} \right)\) và \(C\left( { - 2;4} \right)\)
D.\(D\left( { - 1;1} \right)\) và \(B\left( {2;4} \right)\)

A.\(\dfrac{3}{5}\)
B.\(\dfrac{5}{3}\)
C.\(\dfrac{4}{3}\)
D.\(\dfrac{3}{4}\)

A.\(\left\{ \begin{array}{l}x = 3\\x + 2y = 0\end{array} \right.\)
B.\(\left\{ \begin{array}{l}x + y = 3\\2x + 2y = 9\end{array} \right.\)
C.\(\left\{ \begin{array}{l}x + y = 3\\2y = 0\end{array} \right.\)
D.\(\left\{ \begin{array}{l}x + y = 3\\2x + 2y = 6\end{array} \right.\)

A.\(3cm\)
B.\(4cm\)
C.\(2,5cm\)
D.\(5cm\)

A.\(m = 2\)
B.\(m = 0\)
C.\(m = 1\)
D.\(m =  - 1\)

A.\(\left\{ {1; - 2} \right\}\)
B.\(\left\{ { - 1;\,\,2} \right\}\)
C.\(\left\{ { 1;\,\,2} \right\}\)
D.\(\left\{ { - 1;\,\,-2} \right\}\)

A.\(20cm\)
B.\(18cm\)
C.\(19cm\)
D.\(16cm\)

A.\(R\sqrt 2 \)
B.\(2R\)
C.\(R\sqrt 3 \)
D.\(\dfrac{{3R}}{2}\)