Which of the following is a non-zero vector in the null space of A=(1224)A = \begin{pmatrix} 1 & 2 \\ 2 & 4 \end{pmatrix}A=(1224)?
(21)\begin{pmatrix} 2 \\ 1 \end{pmatrix}(21)
(2−1)\begin{pmatrix} 2 \\ -1 \end{pmatrix}(2−1)
(11)\begin{pmatrix} 1 \\ 1 \end{pmatrix}(11)
(−12)\begin{pmatrix} -1 \\ 2 \end{pmatrix}(−12)