3 and 4 .Determinants and Matrices
easy

નિશ્રાયક $\,\left| {\,\begin{array}{*{20}{c}}{ - 1}&{ - 2}&3\\{ - 4}&{ - 5}&{ - 6}\\{ - 7}&8&9\end{array}\,} \right|$ માં $ -4$ અને $9 $ ના ઉપનિશ્રાયક અને સહઅવયવ અનુક્રમે . . . થાય.

A

$42, 3 ; -42, 3$

B

$-42, -3 ; 42, -3$

C

$42, 3 ; -42, -3$

D

$42, 3; 42, 3$

Solution

(b) Minor of  $-4$ = $\left| {\begin{array}{*{20}{c}}{ – 2}&3\\8&9\end{array}\,} \right| = – 42$,

$9$ = $\left| {\begin{array}{*{20}{c}}{ – 1}&{ – 2}\\{ – 4}&{ – 5}\end{array}} \right| = – 3$

and cofactor of  $ -4$ =${( – 1)^{2 + 1}}( – 42) = 42$,

cofactor of $9$= ${( – 1)^{3 + 3}}( – 3) = – 3$ .

Standard 12
Mathematics

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