Question

If $A=\left[\begin{array}{cc}p& q\\ r& s\end{array}\right]$, ps = 15 and det A =21, then find the value of qr.

Answer 1

$A=\left[\begin{array}{cc}p& q\\ r& s\end{array}\right]$

$detA=ps-qr=21$

$qr=ps-21$

$qr=15-21$

$qr=-6$