Explain why the determinant of each matrix is equal to zero.
(a) $\left[\begin{array}{rrr}2 & -4 & 5 \\ 1 & -2 & 3 \\ 0 & 0 & 0\end{array}\right]$
(b) $\left[\begin{array}{rrrr}4 & -4 & 5 & 7 \\ 2 & -2 & 3 & 1 \\ 4 & -4 & 5 & 7 \\ 6 & 1 & -3 & -3\end{array}\right]$