Biết phương trình \[mx - 5y + 1 = 0\] nhận cặp số \[\left( {1;2} \right)\] làm nghiệm. Giá trị của \[m\] là

A. \[\left\{ \begin{array}{l}x - y = 2\\2x + y = 1\end{array} \right.\].

B. \[\left\{ \begin{array}{l}2x = 0\\x + 5y = 15\end{array} \right.\].

C. \[\left\{ \begin{array}{l}{x^2} - 4{y^2} = 0\\3x + 2y = 7\end{array} \right.\].

D. \[\left\{ \begin{array}{l}2x - y = - 5\\3y + 15 = 0\end{array} \right.\].

A. \(\left( {0;\,\,1} \right)\).

B. \(\left( {1;\,\,0} \right)\).

C. \(\left( {1;\,\,1} \right)\).

D. \(\left( { - 1;\,\,0} \right)\).

A. \(a = 1;\,\,b = 1;\,\,c = 0\).

B. \(a = 1;\,\,b = 2;\,\,c = 1\).

C. \(a = 1;\,\,b = 2;\,\,c = - 1\).

D. \(a = 1;\,\,b = - 2;\,\,c = 1\).

A. \[\left\{ \begin{array}{l}x + y = 3,5\\x + 150y = 500\end{array} \right.\].

B. \[\left\{ \begin{array}{l}x + y = 3,5\\250x + 150y = 500\end{array} \right.\].

C. \[\left\{ \begin{array}{l}x + y = 3,5\\250x + y = 500\end{array} \right.\].

D. \[\left\{ \begin{array}{l}x - y = 3,5\\250x + 150y = 500\end{array} \right.\].

A. \(x + 2y = 1\).

B. \(0x - 0y = 5\).

C. \(0x - y = 3\).

D. \(x + 0y = - 6\).

A. \(y = - 2x + 1\).

B. \(y = 2x - 1\).

C. \[y = \frac{2}{3}x - \frac{1}{3}.\]

D. \[y = \frac{2}{3}x + \frac{1}{3}\].

A. \(\left( {0;\,\,1} \right)\).

B. \(\left( {2;\,\,2} \right)\).

C. \(\left( {3;\,\, - 3} \right)\).

D. \(\left( { - 2;\,\,2} \right)\).