MHT CET · Maths · Matrices
If \(A=\left[\begin{array}{ccc}1 & 0 & 2 \\ -1 & 1 & -2 \\ 0 & 2 & 1\end{array}\right]\), adj \(A=\left[\begin{array}{ccc}5 & x & -2 \\ 1 & 1 & 0 \\ -2 & -2 & y\end{array}\right]\), then value of \(\mathrm{x}+\mathrm{y}\) is
- A 6
- B 3
- C 4
- D 5
Answer & Solution
Correct Answer
(D) 5
Step-by-step Solution
Detailed explanation
\(x\) is element \(a_{12}\) in adj (A)
\(\therefore \mathrm{x}=\) cofactor of \(\mathrm{a}_{21}=(-1)^{2+1}\left|\begin{array}{ll}0 & 2 \\ 2 & 1\end{array}\right|=-(-4)=4\)
Similarly, \(y=(-1)^{3+3}\left|\begin{array}{cc}1 & 0 \\ -1 & 1\end{array}\right|=1 \Rightarrow x+y=5\)
\(\therefore \mathrm{x}=\) cofactor of \(\mathrm{a}_{21}=(-1)^{2+1}\left|\begin{array}{ll}0 & 2 \\ 2 & 1\end{array}\right|=-(-4)=4\)
Similarly, \(y=(-1)^{3+3}\left|\begin{array}{cc}1 & 0 \\ -1 & 1\end{array}\right|=1 \Rightarrow x+y=5\)
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