Question

If $\left[\begin{array}{c}a\\ 8\end{array}\begin{array}{c}5\\ b\end{array}\right]$ $-$ $\left[\begin{array}{c}4\\ 7\end{array}\begin{array}{c}6\\ 2\end{array}\right]$ =$\left[\begin{array}{c}2\\ 1\end{array}\begin{array}{c}-1\\ 5\end{array}\right],$ then value of $a$ is

• A. $a=7$
• B. $b=7$
• C. $a=6$
• D. $b=-7$

Answer 1

The correct option is C $a=6$

Since, $\left[\begin{array}{c}a\\ 8\end{array}\begin{array}{c}5\\ b\end{array}\right]$ $-$ $\left[\begin{array}{c}4\\ 7\end{array}\begin{array}{c}6\\ 2\end{array}\right]$ =$\left[\begin{array}{c}2\\ 1\end{array}\begin{array}{c}-1\\ 5\end{array}\right]$

By equating above matrices, we get

$a-4=2$

$\Rightarrow a=2+4$

$\Rightarrow a=6$