Answer:
-168
Step-by-step explanation:
[tex]\left[\begin{array}{ccc}2&-4&0\\6&5&7\\5&2&0\end{array}\right][/tex]
determinant can be found by cofactor expansion:
say along third column:
[tex]a_{13} \det(\left[\begin{array}{cc}6&5\\5&2\end{array}\right] ) -a_{23} \det \ (\left[\begin{array}{cc}2&-4\\5&2\end{array}\right] ) +a_{33} \det(\left[\begin{array}{cc}2&-4\\6&5\end{array}\right] )[/tex]
[tex]=0 -(7)[(2)(2)-(-4)(5)] +0[/tex]
[tex]=-168[/tex]
