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3 and 4 .Determinants and Matrices
medium
$\lambda$ तथा $\mu$ के क्रमश: मान, जिनके लिए समीकरण निकाय $x+y+z=2$, $x+2 y+3 z=5$, $x+3 y+\lambda z=\mu$ के असंख्य हल हैं
A
$5$ तथा $7$
B
$6$ तथा $8$
C
$4$ तथा $9$
D
$5$ तथा $8$
(JEE MAIN-2020)
Solution
For infinite many solutions
$D=D_{1}=D_{2}=D_{3}=0$
$\operatorname{Now} D =\left|\begin{array}{lll}1 & 1 & 1 \\ 1 & 2 & 3 \\ 1 & 3 & \lambda\end{array}\right|=0$
$1 .(2 \lambda-9)-1 .(\lambda-3)+1 .(3-2)=0$
$\therefore \lambda=5$
$\operatorname{Now} D _{1}=\left|\begin{array}{lll}2 & 1 & 1 \\ 5 & 2 & 3 \\ \mu & 3 & 5\end{array}\right|=0$
$2(10-9)-1(25-3 \mu)+1(15-2 \mu)=0$
$\mu=8$
Standard 12
Mathematics