Question
Evaluate : $\left|\begin{array}{ll}4 & i \\ -2 i & 7\end{array}\right|$ where $\mathrm{i}^2=-1$
✓
Answer
$
\begin{aligned}
\left|\begin{array}{lr}
4 & i \\
-2 i & 7
\end{array}\right| & =4 \times 7-(-2 i) \times i=28+2 i^2 \\
& =28+2(-1)\left[\because \mathrm{i}^2=-1\right] \\
& =28-2=26
\end{aligned}
$
\begin{aligned}
\left|\begin{array}{lr}
4 & i \\
-2 i & 7
\end{array}\right| & =4 \times 7-(-2 i) \times i=28+2 i^2 \\
& =28+2(-1)\left[\because \mathrm{i}^2=-1\right] \\
& =28-2=26
\end{aligned}
$
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