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3 and 4 .Determinants and Matrices
hard
અહી $M=\left\{A=\left(\begin{array}{ll}a & b \\ c & d\end{array}\right): a, b, c, d \in\{\pm 3, \pm 2, \pm 1,0\}\right\} $ આપેલ છે. વિધેય $f: M \rightarrow z$ છે કે જેથી દરેક $A \in M$ માટે $f(A)=\operatorname{det}(A)$ કે જ્યાં $Z$ એ પૂર્ણાંક ગણ છે. તો $f(A)=15$ થાય તેવા $A \in M$ શ્રેણીકોની સંખ્યા મેળવો.
A
$16$
B
$32$
C
$48$
D
$71$
(JEE MAIN-2021)
Solution
$|\mathrm{A}|=\mathrm{ad}-\mathrm{bc}=15$
where $a, b, c, d \in\{\pm 3, \pm 2, \pm 1,0\}$
Case $\mathrm{I} \mathrm{ad}=9 \,\& \,\mathrm{bc}=-6$
For ad possible pairs are $(3,3),(-3,-3)$
For bc possible pairs are $(3,-2),(-3,2),(-2,3),\left(2_{6}-3\right)$
So total matrix $=2 \times 4=8$
Case $II$ ad $=6 \,\&\, \mathrm{bc}=-9$
Similarly total matrix $=2 \times 4=8$
$\Rightarrow$ Total such matrices are $=16$
Standard 12
Mathematics
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