Question

$If$ $\left|\begin{array}{ccc}1& 0& 0\\ 2& 3& 4\\ 5& -6& x\end{array}\right|$ $=45$ $then$ $x=$

• A. $4$
• B. $7$
• C. $-5$
• D. $-7$

Answer 1

Answer: (B)

$7$

Given $\left|\begin{array}{ccc}1& 0& 0\\ 2& 3& 4\\ 5& -6& x\end{array}\right|=45$
By operation of matrix (5),
$1(3x+24)=45$
$3x=21$
$\Rightarrow x=7$