If A=bmatrix 2 & 1 \\ 7 & 5 bmatrix, then the value of, A(adj A), is Option 1: 3 Option 2: 9 Option 3: 27 Option 4: 81

Answer: 9. Solution: Here, A, = 10-7 = 3. Since A(adj A) =, A, I, we get, A(adj A), =, A, I_2, =, A, ^2 for a 2x2 matrix. Hence the value is 3^2 = 9.

Algebra

Matrices & Determinants

Easy

applied

If $A=\begin{bmatrix} 2 & 1 \\ 7 & 5 \end{bmatrix}$ , then the value of $|A(adj A)|$ is

✅ Correct Option: 2

Here $|A| = 10-7 = 3$ .

Since $A(adj A) = |A|I$ , we get $|A(adj A)| = |\,|A|I_2| = |A|^2$ for a $2\times2$ matrix.

Hence the value is $3^2 = 9$ .

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