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3 and 4 .Determinants and Matrices
medium
If the system of linear equations $3 x+y+\beta z=3$, $2 x+\alpha y-z=-3$, $x+2 y+z=4$ has infinitely many solutions, then the value of $22 \beta-9 \alpha$ is :
A$49$
B$31$
C$43$
D$37$
(JEE MAIN-2025)
Solution
$\Delta=\left|\begin{array}{ccc}3 & 1 & \beta \\ 2 & \alpha & -1 \\ 1 & 2 & 1\end{array}\right|=0$
$3 \alpha+4 \beta-\alpha \beta+3=0$
$\Delta_3=\left|\begin{array}{ccc}3 & 1 & 3 \\ 2 & \alpha & -3 \\ 1 & 2 & 4\end{array}\right|=0$
$9 \alpha+19=0$
$\alpha=\frac{-19}{9}, \beta=\frac{6}{11}$
$\Rightarrow 22 \beta-9 \alpha=31$
$3 \alpha+4 \beta-\alpha \beta+3=0$
$\Delta_3=\left|\begin{array}{ccc}3 & 1 & 3 \\ 2 & \alpha & -3 \\ 1 & 2 & 4\end{array}\right|=0$
$9 \alpha+19=0$
$\alpha=\frac{-19}{9}, \beta=\frac{6}{11}$
$\Rightarrow 22 \beta-9 \alpha=31$
Standard 12
Mathematics