যদি \( A = \begin{bmatrix} -1 & -3 \\ 2 & 4 \end{bmatrix} \) হয়, তাহলে \( | \text{Adj}(A) | \) কত হবে?
JUUnit-ASet-3উচ্চতর গণিত প্রথম পত্রম্যাট্রিক্স ও নির্ণায়কনির্ণায়ক ও নির্ণায়কের ধর্মাবলি (Topic Practice)JU - ⚡ অনলাইন প্রশ্নব্যাংক দেখুন 💥
সঠিক উত্তরঃ
B.
1000
Another Explanation (5):
Given matrix \( A = \begin{bmatrix} -1 & -3 \\ 2 & 4 \end{bmatrix} \)
Step 1: Find \( \det(A) \)
\[
\det(A) = (-1)(4) - (-3)(2) = -4 + 6 = 2
\]
Step 2: Find \( \text{Adj}(A) \)
\[
\text{Adj}(A) = (\det(A)) \times A^{-1}
\]
But more straightforwardly, for a 2x2 matrix:
\[
\text{Adj}(A) = \begin{bmatrix} d & -b \\ -c & a \end{bmatrix}
\]
where \( A = \begin{bmatrix} a & b \\ c & d \end{bmatrix} \)
So,
\[
a = -1, \quad b = -3, \quad c = 2, \quad d = 4
\]
\[
\text{Adj}(A) = \begin{bmatrix} 4 & 3 \\ -2 & -1 \end{bmatrix}
\]
Step 3: Find \( |\text{Adj}(A)| \)
\[
|\text{Adj}(A)| = (4)(-1) - (3)(-2) = -4 + 6 = 2
\]
**Note:** The problem asks for \( |\text{Adj}(A)| \), but the answer provided is 1000, which suggests there might be a different interpretation or typo.
Alternatively, considering the relation:
\[
\text{For a 2x2 matrix } A, \quad |\text{Adj}(A)| = |\det(A) \times A^{-1}| = |\det(A)|^2
\]
since \( |\text{Adj}(A)| = |\det(A)|^{n-1} \) for an \( n \times n \) matrix, and in 2x2:
\[
|\text{Adj}(A)| = |\det(A)|^{2-1} = |\det(A)| = 2
\]
But this conflicts with the earlier calculation.
Alternatively, for any invertible matrix:
\[
\text{Adj}(A) = (\det A) \times A^{-1}
\]
and the determinant of \( \text{Adj}(A) \) is:
\[
|\text{Adj}(A)| = |\det A|^{n-1} \times |\det A| = |\det A|^{n}
\]
for an \( n \times n \) matrix, so in 2x2:
\[
|\text{Adj}(A)| = |\det A|^{2} = 2^{2} = 4
\]
This aligns with the standard property:
\[
|\text{Adj}(A)| = |\det(A)|^{n-1}
\]
for \( n \times n \) matrices.
Hence, the correct calculation:
\[
|\text{Adj}(A)| = |\det(A)|^{2-1} = |\det(A)| = 2
\]
But the provided answer is 1000, which suggests the problem expects the calculation:
\[
|\text{Adj}(A)| = |\det(A)|^{n-1} \times |\det(A)| = |\det(A)|^{n} = 2^{2} = 4
\]
Given the inconsistency, perhaps the intention is:
\[
|\text{Adj}(A)| = |\det(A)|^{n-1} \times |\det(A)| = |\det(A)|^{n} = 2^{2} = 4
\]
Yet, the answer is 1000, which is \( 10^3 \). Suppose the eigenvalues or specific calculations lead to that.
Alternatively, considering the general property:
\[
|\text{Adj}(A)| = |\det(A)|^{n-1}
\]
for an \( n \times n \) matrix.
In this case, \( |\det(A)| = 2 \), so:
\[
|\text{Adj}(A)| = 2^{2-1} = 2
\]
Since the answer is given as 1000, perhaps the question involves the matrix \( A \) scaled or different.
**Final conclusion:**
Given the data and standard properties, the most consistent calculation yields:
|Adj(A)| = |\det(A)|^{n-1} = 2^{1} = 2
But since the user states the answer is "1000," perhaps they are considering:
\[
| \text{Adj}(A)| = |\det(A)|^{n} = 2^{2} = 4
\]
or a different interpretation.
**Therefore, the formal mathematical answer is:**
|Adj(A)| = |\det(A)|^{n-1} = 2^{2-1} = 2