3 and 4 .Determinants and Matrices
easy

यदि $A =\left[\begin{array}{ccc}1 & 1 & -2 \\ 2 & 1 & -3 \\ 5 & 4 & -9\end{array}\right],$ हो तो $| A |$ ज्ञात कीजिए।

A

$1$

B

$2$

C

$0$

D

$3$

Solution

Let $A=\left[\begin{array}{lll}1 & 1 & -2 \\ 2 & 1 & -3 \\ 5 & 4 & -9\end{array}\right]$

By expanding along the first row, we have:

$A=\left[\begin{array}{lll}1 & 1 & -2 \\ 2 & 1 & -3 \\ 5 & 4 & -9\end{array}\right]$

$|A|=1\left|\begin{array}{cc}1 & -3 \\ 4 & -9\end{array}\right|-1\left|\begin{array}{cc}2 & -3 \\ 5 & -9\end{array}\right|-2\left|\begin{array}{cc}2 & 1 \\ 5 & 4\end{array}\right|$

$=1(-9+12)-1(-18+15)-2(8-5)$

$=1(3)-1(-3)-2(3)$

$=3+3-6$

$=6-6$

$=0$

Standard 12
Mathematics

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