Question

помогите плиз :0000000

Answer 1

$\left|\begin{array}{cccc}-1&a&2&1\\1&-1&1&4\\-2&3&3&0\\1&2&3&1\end{array}\right|=-a\cdot \left|\begin{array}{ccc}1&1&4\\-2&3&0\\1&3&1\end{array}\right|=\\\\\\=-a\cdot \Big (1\cdot 3-1\cdot (-2)+4\cdot (-6-3)\Big )=-a\cdot (3+2-36)=31a=0\; \; \Rightarrow \\\\a=0$