Question:
Find the value of the determinant $\left[\begin{array}{ll}4200 & 4201 \\ 4205 & 4203\end{array}\right]$.
Solution:
Let $\Delta=\mid \begin{array}{ll}4200 & 4201\end{array}$
$\begin{array}{ll}4202 & 4203 \mid\end{array}$
$\Delta=\mid 42001$
42021 [Applying $C_{2} \rightarrow C_{2}-C_{1}$ ]
$=4200-4202$
$=-2$
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