Question

$\left| \begin{matrix} 5 & 3 & - 1 \

• 7 & x & - 3 \ 9 & 6 & - 2 \end{matrix} \right| = 0$, then x is equal to .

• A. 3
• B. 5
• C. 7
• D. 9

Answer 1

Answer: (D)

9

Answer 2

We have $\Delta = \left| \begin{matrix} 5 & 3 & - 1 \

• 7 & x & - 3 \ 9 & 6 & - 2 \end{matrix} \right|\ = 0$

$\therefore$ $- 10x + 90 - 42 - 81 + 42 + 9x = 0\text{or}\ x = 9$.