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CBSE - Class 12 Mathematics Matrices Worksheet
EXERCISE 3.3
Worksheet Answers
Solution:
Given matrices $A$ and $B$, the difference $A - B$ is calculated by subtracting corresponding elements: $C_{ij} = A_{ij} - B_{ij}$.
$A - B = \begin{bmatrix} -1 & 2 & 3 \\ 5 & 7 & 9 \\ -2 & 1 & 1 \end{bmatrix} - \begin{bmatrix} -4 & 1 & -5 \\ 1 & 2 & 0 \\ 1 & 3 & 1 \end{bmatrix}$
$A - B = \begin{bmatrix} (-1 - (-4)) & (2 - 1) & (3 - (-5)) \\ (5 - 1) & (7 - 2) & (9 - 0) \\ (-2 - 1) & (1 - 3) & (1 - 1) \end{bmatrix} = \begin{bmatrix} 3 & 1 & 8 \\ 4 & 5 & 9 \\ -3 & -2 & 0 \end{bmatrix}$
The transpose of a matrix, denoted by $M'$, is obtained by swapping rows and columns ($M'_{ij} = M_{ji}$). [Per the definition of Matrix Transpose].
$(A - B)' = \begin{bmatrix} 3 & 4 & -3 \\ 1 & 5 & -2 \\ 8 & 9 & 0 \end{bmatrix}$
We transform both initial matrices by interchanging rows and columns:
$A' = \begin{bmatrix} -1 & 5 & -2 \\ 2 & 7 & 1 \\ 3 & 9 & 1 \end{bmatrix}$
$B' = \begin{bmatrix} -4 & 1 & 1 \\ 1 & 2 & 3 \\ -5 & 0 & 1 \end{bmatrix}$
Perform element-wise subtraction on the transposed matrices:
$A' - B' = \begin{bmatrix} (-1 - (-4)) & (5 - 1) & (-2 - 1) \\ (2 - 1) & (7 - 2) & (1 - 3) \\ (3 - (-5)) & (9 - 0) & (1 - 1) \end{bmatrix}$
$A' - B' = \begin{bmatrix} 3 & 4 & -3 \\ 1 & 5 & -2 \\ 8 & 9 & 0 \end{bmatrix}$
Comparing the result from Step 2 and Step 4:
| Expression | Resultant Matrix |
|---|---|
| $(A - B)'$ | $\begin{bmatrix} 3 & 4 & -3 \\ 1 & 5 & -2 \\ 8 & 9 & 0 \end{bmatrix}$ |
| $A' - B'$ | $\begin{bmatrix} 3 & 4 & -3 \\ 1 & 5 & -2 \\ 8 & 9 & 0 \end{bmatrix}$ |
[By the Property of Transpose of Matrices: $(A \pm B)' = A' \pm B'$]. Since both matrices are identical element-wise, the identity is verified.
Final Solution: $(A - B)' = A' - B' = \begin{bmatrix} 3 & 4 & -3 \\ 1 & 5 & -2 \\ 8 & 9 & 0 \end{bmatrix}$
Solution:
Any square matrix $A$ can be uniquely expressed as the sum of a symmetric matrix $P$ and a skew-symmetric matrix $Q$, defined by the following theorem [Per the Theorem on Decomposition of Matrices]:
$A = P + Q$, where:
Let $A = \begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix}$.
To find the transpose $A^T$, we interchange rows and columns [Definition of Transpose]:
$A^T = \begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix}$.
$P = \frac{1}{2}(A + A^T)$
$P = \frac{1}{2} \left( \begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix} + \begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix} \right)$
$P = \frac{1}{2} \begin{bmatrix} 12 & -4 & 4 \\ -4 & 6 & -2 \\ 4 & -2 & 6 \end{bmatrix} = \begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix}$.
[Justification: $P^T = P$, confirming $P$ is symmetric].
$Q = \frac{1}{2}(A - A^T)$
$Q = \frac{1}{2} \left( \begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix} - \begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix} \right)$
$Q = \frac{1}{2} \begin{bmatrix} 0 & 0 & 0 \\ 0 & 0 & 0 \\ 0 & 0 & 0 \end{bmatrix} = \begin{bmatrix} 0 & 0 & 0 \\ 0 & 0 & 0 \\ 0 & 0 & 0 \end{bmatrix}$.
[Justification: $Q^T = -Q$, confirming $Q$ is skew-symmetric].
The matrix $A$ expressed as the sum of a symmetric and a skew-symmetric matrix is $A = P + Q$:
$\begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix} = \begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix} + \begin{bmatrix} 0 & 0 & 0 \\ 0 & 0 & 0 \\ 0 & 0 & 0 \end{bmatrix}$
Final Solution: The matrix $A$ is equal to itself (symmetric) plus a null matrix (skew-symmetric). The result is $\begin{bmatrix} 6 & -2 & 2 \\ -2 & 3 & -1 \\ 2 & -1 & 3 \end{bmatrix} + \begin{bmatrix} 0 & 0 & 0 \\ 0 & 0 & 0 \\ 0 & 0 & 0 \end{bmatrix}$.
Solution:
Let the given matrix be $A$.
$A = \begin{bmatrix} 3 & 5 \\ 1 & -1 \end{bmatrix}$
Any square matrix $A$ can be expressed as the sum of a symmetric matrix $P$ and a skew-symmetric matrix $Q$, where:
$A = P + Q$
$P = \frac{1}{2}(A + A^T)$ [Definition of a symmetric matrix]
$Q = \frac{1}{2}(A - A^T)$ [Definition of a skew-symmetric matrix]
To find the transpose, interchange the rows and columns of matrix $A$:
$A^T = \begin{bmatrix} 3 & 1 \\ 5 & -1 \end{bmatrix}$
First, compute the sum $A + A^T$:
$A + A^T = \begin{bmatrix} 3 & 5 \\ 1 & -1 \end{bmatrix} + \begin{bmatrix} 3 & 1 \\ 5 & -1 \end{bmatrix} = \begin{bmatrix} 3+3 & 5+1 \\ 1+5 & -1-1 \end{bmatrix} = \begin{bmatrix} 6 & 6 \\ 6 & -2 \end{bmatrix}$
Now, multiply by the scalar $\frac{1}{2}$:
$P = \frac{1}{2} \begin{bmatrix} 6 & 6 \\ 6 & -2 \end{bmatrix} = \begin{bmatrix} 3 & 3 \\ 3 & -1 \end{bmatrix}$
[Verification: $P^T = \begin{bmatrix} 3 & 3 \\ 3 & -1 \end{bmatrix} = P$, which satisfies the condition for symmetry.]
First, compute the difference $A - A^T$:
$A - A^T = \begin{bmatrix} 3 & 5 \\ 1 & -1 \end{bmatrix} - \begin{bmatrix} 3 & 1 \\ 5 & -1 \end{bmatrix} = \begin{bmatrix} 3-3 & 5-1 \\ 1-5 & -1-(-1) \end{bmatrix} = \begin{bmatrix} 0 & 4 \\ -4 & 0 \end{bmatrix}$
Now, multiply by the scalar $\frac{1}{2}$:
$Q = \frac{1}{2} \begin{bmatrix} 0 & 4 \\ -4 & 0 \end{bmatrix} = \begin{bmatrix} 0 & 2 \\ -2 & 0 \end{bmatrix}$
[Verification: $Q^T = \begin{bmatrix} 0 & -2 \\ 2 & 0 \end{bmatrix} = -Q$, which satisfies the condition for skew-symmetry.]
Combining the matrices calculated in Step 2 and Step 3:
$A = \begin{bmatrix} 3 & 3 \\ 3 & -1 \end{bmatrix} + \begin{bmatrix} 0 & 2 \\ -2 & 0 \end{bmatrix}$
Final Solution: $\begin{bmatrix} 3 & 5 \\ 1 & -1 \end{bmatrix} = \begin{bmatrix} 3 & 3 \\ 3 & -1 \end{bmatrix} + \begin{bmatrix} 0 & 2 \\ -2 & 0 \end{bmatrix}$
Solution:
Given $A' = \begin{bmatrix} 3 & 4 \\ -1 & 2 \\ 0 & 1 \end{bmatrix}$. By the property of transpose, $(A')' = A$ [Per the definition of Matrix Transpose: $(A^T)_{ij} = A_{ji}$].
Transposing the rows of $A'$ into columns, we obtain:
$A = \begin{bmatrix} 3 & -1 & 0 \\ 4 & 2 & 1 \end{bmatrix}$
Given $B = \begin{bmatrix} -1 & 2 & 1 \\ 1 & 2 & 3 \end{bmatrix}$. Since $A$ is of order $2 \times 3$ and $B$ is of order $2 \times 3$, the sum $A+B$ is defined [Per the Condition for Matrix Addition: Matrices must have identical dimensions].
$A + B = \begin{bmatrix} 3 + (-1) & -1 + 2 & 0 + 1 \\ 4 + 1 & 2 + 2 & 1 + 3 \end{bmatrix}$
$A + B = \begin{bmatrix} 2 & 1 & 1 \\ 5 & 4 & 4 \end{bmatrix}$
Taking the transpose of the sum calculated in Step 2:
$(A + B)' = \begin{bmatrix} 2 & 5 \\ 1 & 4 \\ 1 & 4 \end{bmatrix}$
We are given $A' = \begin{bmatrix} 3 & 4 \\ -1 & 2 \\ 0 & 1 \end{bmatrix}$.
First, calculate $B'$ by transposing $B = \begin{bmatrix} -1 & 2 & 1 \\ 1 & 2 & 3 \end{bmatrix}$:
$B' = \begin{bmatrix} -1 & 1 \\ 2 & 2 \\ 1 & 3 \end{bmatrix}$
Now, perform the addition $A' + B'$:
$A' + B' = \begin{bmatrix} 3 + (-1) & 4 + 1 \\ -1 + 2 & 2 + 2 \\ 0 + 1 & 1 + 3 \end{bmatrix} = \begin{bmatrix} 2 & 5 \\ 1 & 4 \\ 1 & 4 \end{bmatrix}$
| Expression | Resultant Matrix |
|---|---|
| LHS: $(A + B)'$ | $\begin{bmatrix} 2 & 5 \\ 1 & 4 \\ 1 & 4 \end{bmatrix}$ |
| RHS: $A' + B'$ | $\begin{bmatrix} 2 & 5 \\ 1 & 4 \\ 1 & 4 \end{bmatrix}$ |
Since the resulting matrices are identical in both entries and dimensions, the property $(A + B)' = A' + B'$ is verified [Per the Theorem of Transpose of Sums].
Final Solution: $(A + B)' = A' + B' = \begin{bmatrix} 2 & 5 \\ 1 & 4 \\ 1 & 4 \end{bmatrix}$
Solution:
For any given matrix $A$ of order $m \times n$, the transpose of the matrix, denoted by $A^T$ or $A'$, is defined as an $n \times m$ matrix obtained by interchanging the rows and columns of $A$. Specifically, if $A = [a_{ij}]$, then $A^T = [a_{ji}]$, where the element at position $(i, j)$ in $A$ moves to position $(j, i)$ in $A^T$ [Per the definition of transpose in linear algebra].
Let the given matrix $A$ be defined as follows:
$A = \begin{bmatrix} 1 & -1 \\ 2 & 3 \end{bmatrix}$To obtain $A^T$, we perform the following mapping:
Consequently, the elements are rearranged such that the element originally in the $(i, j)$ position is placed in the $(j, i)$ position.
Substituting the values into the new structure:
$A^T = \begin{bmatrix} a_{11} & a_{21} \\ a_{12} & a_{22} \end{bmatrix}$Final Solution: The transpose of the matrix $\begin{bmatrix} 1 & -1 \\ 2 & 3 \end{bmatrix}$ is $\begin{bmatrix} 1 & 2 \\ -1 & 3 \end{bmatrix}$.
Solution:
Given the matrix $A$:
$A = \begin{bmatrix} \sin \alpha & \cos \alpha \\ -\cos \alpha & \sin \alpha \end{bmatrix}$
The transpose of a matrix, denoted as $A'$, is obtained by interchanging the rows and columns of $A$ [Per the Definition of Matrix Transposition].
$A' = \begin{bmatrix} \sin \alpha & -\cos \alpha \\ \cos \alpha & \sin \alpha \end{bmatrix}$
To verify the identity, we compute the product of $A'$ and $A$:
$A' A = \begin{bmatrix} \sin \alpha & -\cos \alpha \\ \cos \alpha & \sin \alpha \end{bmatrix} \begin{bmatrix} \sin \alpha & \cos \alpha \\ -\cos \alpha & \sin \alpha \end{bmatrix}$
Following the rule of matrix multiplication (Row $\times$ Column) [Per the Matrix Multiplication Row-Column Rule]:
| Element Position | Calculation |
|---|---|
| (1, 1) | $(\sin \alpha)(\sin \alpha) + (-\cos \alpha)(-\cos \alpha) = \sin^2 \alpha + \cos^2 \alpha$ |
| (1, 2) | $(\sin \alpha)(\cos \alpha) + (-\cos \alpha)(\sin \alpha) = \sin \alpha \cos \alpha - \sin \alpha \cos \alpha$ |
| (2, 1) | $(\cos \alpha)(\sin \alpha) + (\sin \alpha)(-\cos \alpha) = \sin \alpha \cos \alpha - \sin \alpha \cos \alpha$ |
| (2, 2) | $(\cos \alpha)(\cos \alpha) + (\sin \alpha)(\sin \alpha) = \cos^2 \alpha + \sin^2 \alpha$ |
Applying the Pythagorean identity $\sin^2 \theta + \cos^2 \theta = 1$ [Per the Fundamental Trigonometric Identity]:
$A' A = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}$
Since $\begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} = I$ (the identity matrix of order 2), the condition $A' A = I$ is satisfied.
Final Solution: $A' A = I$, which confirms that the given matrix $A$ is an orthogonal matrix.
Solution:
The transpose of a matrix $A$, denoted by $A^T$ or $A'$, is obtained by interchanging the rows and columns of the original matrix. Formally, if $A = [a_{ij}]_{m \times n}$, then $A^T = [a_{ji}]_{n \times m}$. [Per the definition of Transpose of a Matrix in Linear Algebra].
Given the matrix $A$ of order $3 \times 3$:
$A = \begin{bmatrix} -1 & 5 & 6 \\ \sqrt{3} & 5 & 6 \\ 2 & 3 & -1 \end{bmatrix}$
To compute $A^T$, we assign the elements of the first row to the first column, the second row to the second column, and the third row to the third column.
| Original Row Index ($i$) | Original Elements | Transposed Column Index ($j$) |
|---|---|---|
| Row 1 | $[-1, 5, 6]$ | Column 1 |
| Row 2 | $[\sqrt{3}, 5, 6]$ | Column 2 |
| Row 3 | $[2, 3, -1]$ | Column 3 |
Placing these into the transposed matrix structure:
$A^T = \begin{bmatrix} -1 & \sqrt{3} & 2 \\ 5 & 5 & 3 \\ 6 & 6 & -1 \end{bmatrix}$
Final Solution: The transpose of the matrix is $\begin{bmatrix} -1 & \sqrt{3} & 2 \\ 5 & 5 & 3 \\ 6 & 6 & -1 \end{bmatrix}$
Solution:
The matrix $A$ is defined as: $A = \begin{bmatrix} 0 & 1 & -1 \\ -1 & 0 & 1 \\ 1 & -1 & 0 \end{bmatrix}$
To prove that $A$ is a skew-symmetric matrix, we must demonstrate that $A^T = -A$, where $A^T$ is the transpose of matrix $A$ [Per the definition of skew-symmetric matrices].
To find the transpose $A^T$, we interchange the rows and columns of matrix $A$ [By the definition of Matrix Transpose, where $(A^T)_{ij} = A_{ji}$].
$A^T = \begin{bmatrix} 0 & -1 & 1 \\ 1 & 0 & -1 \\ -1 & 1 & 0 \end{bmatrix}$
To find $-A$, we multiply every element of matrix $A$ by the scalar $-1$ [Per the property of Scalar Multiplication of matrices].
$-A = -1 \cdot \begin{bmatrix} 0 & 1 & -1 \\ -1 & 0 & 1 \\ 1 & -1 & 0 \end{bmatrix} = \begin{bmatrix} -(0) & -(1) & -(-1) \\ -(-1) & -(0) & -(1) \\ -(1) & -(-1) & -(0) \end{bmatrix}$
$-A = \begin{bmatrix} 0 & -1 & 1 \\ 1 & 0 & -1 \\ -1 & 1 & 0 \end{bmatrix}$
| Matrix | Result |
|---|---|
| $A^T$ | $\begin{bmatrix} 0 & -1 & 1 \\ 1 & 0 & -1 \\ -1 & 1 & 0 \end{bmatrix}$ |
| $-A$ | $\begin{bmatrix} 0 & -1 & 1 \\ 1 & 0 & -1 \\ -1 & 1 & 0 \end{bmatrix}$ |
Since $A^T = -A$, the condition for a skew-symmetric matrix is satisfied [By the formal definition of skew-symmetry: $A^T = -A$]. Furthermore, note that the diagonal elements are all zero, which is a necessary condition for a skew-symmetric matrix.
Final Solution: Since $A^T = -A$, the matrix $A$ is proven to be a skew-symmetric matrix.
Solution:
A square matrix $A$ is defined as a symmetric matrix if and only if the transpose of the matrix $A$ is equal to the matrix itself. Mathematically, this condition is expressed as:
$A^T = A$
[Definition of Symmetric Matrix: A square matrix $A = [a_{ij}]$ is symmetric if $a_{ij} = a_{ji}$ for all $i, j$.]
Given the matrix:
$A = \begin{bmatrix} 1 & -1 & 5 \\ -1 & 2 & 1 \\ 5 & 1 & 3 \end{bmatrix}$
To find the transpose $A^T$, we convert the rows of matrix $A$ into the columns of matrix $A^T$.
$A^T = \begin{bmatrix} 1 & -1 & 5 \\ -1 & 2 & 1 \\ 5 & 1 & 3 \end{bmatrix}$
We compare the elements of $A$ and $A^T$ position-wise ($a_{ij}$ with $a_{ji}$):
| Element Position | $a_{ij}$ (Original) | $a_{ji}$ (Transpose) |
|---|---|---|
| (1,2) and (2,1) | $-1$ | $-1$ |
| (1,3) and (3,1) | $5$ | $5$ |
| (2,3) and (3,2) | $1$ | $1$ |
Since $a_{ij} = a_{ji}$ for all $i, j \in \{1, 2, 3\}$, it is evident that $A^T = A$.
Final Solution: Since the transpose of the matrix $A$ is identical to the original matrix $A$ ($A^T = A$), the matrix $A$ is confirmed to be a symmetric matrix.
Solution:
The transpose of a matrix, denoted as $A^T$ or $A'$, is an operation that converts rows into columns and columns into rows. For any matrix $A$ of order $m \times n$, its transpose $A^T$ will have the order $n \times m$. Formally, if $A = [a_{ij}]$, then $A^T = [a_{ji}]$, where the element at the $i$-th row and $j$-th column is shifted to the $j$-th row and $i$-th column [By the definition of matrix transpose].
Let the given matrix be $A$. $A = \begin{bmatrix} 5 \\ \frac{1}{2} \\ -1 \end{bmatrix}$
To compute $A^T$, we take the column vector and rewrite it as a row vector:
$A^T = \begin{bmatrix} 5 & \frac{1}{2} & -1 \end{bmatrix}$
Final Solution: The transpose of the matrix $\begin{bmatrix} 5 \\ \frac{1}{2} \\ -1 \end{bmatrix}$ is $\begin{bmatrix} 5 & \frac{1}{2} & -1 \end{bmatrix}$.
Solution:
Given the transpose of matrix $A$, denoted as $A' = \begin{bmatrix} -2 & 3 \\ 1 & 2 \end{bmatrix}$, we find $A$ by applying the property of transposition: $(A')' = A$ [Property: The transpose of a transpose is the original matrix].
Thus, transposing the rows and columns of $A'$:
$A = \begin{bmatrix} -2 & 1 \\ 3 & 2 \end{bmatrix}$
Given $B = \begin{bmatrix} -1 & 0 \\ 1 & 2 \end{bmatrix}$, we perform scalar multiplication by multiplying every element of the matrix by the scalar $2$ [Definition of Scalar Multiplication]:
$2B = 2 \times \begin{bmatrix} -1 & 0 \\ 1 & 2 \end{bmatrix} = \begin{bmatrix} 2(-1) & 2(0) \\ 2(1) & 2(2) \end{bmatrix} = \begin{bmatrix} -2 & 0 \\ 2 & 4 \end{bmatrix}$
To find the sum of matrices $A$ and $2B$, we add the corresponding elements [Property: Matrix addition is defined for matrices of the same order]:
$A + 2B = \begin{bmatrix} -2 & 1 \\ 3 & 2 \end{bmatrix} + \begin{bmatrix} -2 & 0 \\ 2 & 4 \end{bmatrix}$
$A + 2B = \begin{bmatrix} -2 + (-2) & 1 + 0 \\ 3 + 2 & 2 + 4 \end{bmatrix} = \begin{bmatrix} -4 & 1 \\ 5 & 6 \end{bmatrix}$
To find the transpose, we interchange the rows and columns of the resulting matrix from Step 3 [Definition: If $C = [c_{ij}]$, then $C' = [c_{ji}]$]:
$(A + 2B)' = \begin{bmatrix} -4 & 5 \\ 1 & 6 \end{bmatrix}$
Final Solution: $(A + 2B)' = \begin{bmatrix} -4 & 5 \\ 1 & 6 \end{bmatrix}$
Solution:
Given the matrix $A$ of order $2 \times 2$:
$A = \begin{bmatrix} 1 & 5 \\ 6 & 7 \end{bmatrix}$
The transpose of a matrix, denoted as $A'$, is obtained by interchanging its rows and columns [Per the definition of Matrix Transposition, where $A'_{ij} = A_{ji}$].
$A' = \begin{bmatrix} 1 & 6 \\ 5 & 7 \end{bmatrix}$
To compute the sum, we perform element-wise addition [Per the Matrix Addition Property]:
$(A + A') = \begin{bmatrix} 1 & 5 \\ 6 & 7 \end{bmatrix} + \begin{bmatrix} 1 & 6 \\ 5 & 7 \end{bmatrix}$
$(A + A') = \begin{bmatrix} (1 + 1) & (5 + 6) \\ (6 + 5) & (7 + 7) \end{bmatrix}$
$(A + A') = \begin{bmatrix} 2 & 11 \\ 11 & 14 \end{bmatrix}$
A matrix $M$ is defined as symmetric if and only if $M' = M$ [By the definition of a Symmetric Matrix]. Let $S = (A + A')$. We must verify if $S' = S$.
Taking the transpose of $S$:
$S = \begin{bmatrix} 2 & 11 \\ 11 & 14 \end{bmatrix}$
$S' = \begin{bmatrix} 2 & 11 \\ 11 & 14 \end{bmatrix}$
Comparing $S'$ and $S$, we observe that $S'_{ij} = S_{ij}$ for all $i, j$ [Verification via identity of matrix components].
Final Solution: Since $(A + A')' = (A + A')$, the matrix $(A + A')$ is proven to be a symmetric matrix.
Solution:
Any square matrix $A$ can be uniquely expressed as the sum of a symmetric matrix $P$ and a skew-symmetric matrix $Q$, defined as follows [Per the Theorem on Decomposition of Matrices]:
$A = P + Q$
Where:
Given $A = \begin{bmatrix} 3 & 3 & -1 \\ -2 & -2 & 1 \\ -4 & -5 & 2 \end{bmatrix}$
The transpose $A^T$ is obtained by interchanging rows and columns:
$A^T = \begin{bmatrix} 3 & -2 & -4 \\ 3 & -2 & -5 \\ -1 & 1 & 2 \end{bmatrix}$
$P = \frac{1}{2}(A + A^T) = \frac{1}{2} \left( \begin{bmatrix} 3 & 3 & -1 \\ -2 & -2 & 1 \\ -4 & -5 & 2 \end{bmatrix} + \begin{bmatrix} 3 & -2 & -4 \\ 3 & -2 & -5 \\ -1 & 1 & 2 \end{bmatrix} \right)$
$P = \frac{1}{2} \begin{bmatrix} 6 & 1 & -5 \\ 1 & -4 & -4 \\ -5 & -4 & 4 \end{bmatrix} = \begin{bmatrix} 3 & 0.5 & -2.5 \\ 0.5 & -2 & -2 \\ -2.5 & -2 & 2 \end{bmatrix}$
$Q = \frac{1}{2}(A - A^T) = \frac{1}{2} \left( \begin{bmatrix} 3 & 3 & -1 \\ -2 & -2 & 1 \\ -4 & -5 & 2 \end{bmatrix} - \begin{bmatrix} 3 & -2 & -4 \\ 3 & -2 & -5 \\ -1 & 1 & 2 \end{bmatrix} \right)$
$Q = \frac{1}{2} \begin{bmatrix} 0 & 5 & 3 \\ -5 & 0 & 6 \\ -3 & -6 & 0 \end{bmatrix} = \begin{bmatrix} 0 & 2.5 & 1.5 \\ -2.5 & 0 & 3 \\ -1.5 & -3 & 0 \end{bmatrix}$
To verify the decomposition, sum $P$ and $Q$:
$P + Q = \begin{bmatrix} 3 & 0.5 & -2.5 \\ 0.5 & -2 & -2 \\ -2.5 & -2 & 2 \end{bmatrix} + \begin{bmatrix} 0 & 2.5 & 1.5 \\ -2.5 & 0 & 3 \\ -1.5 & -3 & 0 \end{bmatrix} = \begin{bmatrix} 3 & 3 & -1 \\ -2 & -2 & 1 \\ -4 & -5 & 2 \end{bmatrix} = A$
Final Solution: The matrix is expressed as the sum of the symmetric matrix $\begin{bmatrix} 3 & 0.5 & -2.5 \\ 0.5 & -2 & -2 \\ -2.5 & -2 & 2 \end{bmatrix}$ and the skew-symmetric matrix $\begin{bmatrix} 0 & 2.5 & 1.5 \\ -2.5 & 0 & 3 \\ -1.5 & -3 & 0 \end{bmatrix}$.
Solution:
We are given the matrices:
$A = \begin{bmatrix} 1 \\ -4 \\ 3 \end{bmatrix}$ (Order: $3 \times 1$)
$B = \begin{bmatrix} -1 & 2 & 1 \end{bmatrix}$ (Order: $1 \times 3$)
[Per the definition of matrix multiplication, the product $AB$ is defined if the number of columns in $A$ equals the number of rows in $B$. Since $A$ is $3 \times 1$ and $B$ is $1 \times 3$, the resulting matrix $AB$ will be of order $3 \times 3$.]
Applying the row-by-column multiplication rule:
$AB = \begin{bmatrix} 1 \\ -4 \\ 3 \end{bmatrix} \begin{bmatrix} -1 & 2 & 1 \end{bmatrix} = \begin{bmatrix} (1)(-1) & (1)(2) & (1)(1) \\ (-4)(-1) & (-4)(2) & (-4)(1) \\ (3)(-1) & (3)(2) & (3)(1) \end{bmatrix}$
$AB = \begin{bmatrix} -1 & 2 & 1 \\ 4 & -8 & -4 \\ -3 & 6 & 3 \end{bmatrix}$
To find the transpose, we interchange rows and columns [Per the definition of Transpose Matrix $(A^T)_{ij} = A_{ji}$]:
$(AB)' = \begin{bmatrix} -1 & 4 & -3 \\ 2 & -8 & 6 \\ 1 & -4 & 3 \end{bmatrix}$
For $A = \begin{bmatrix} 1 \\ -4 \\ 3 \end{bmatrix}$, the transpose $A' = \begin{bmatrix} 1 & -4 & 3 \end{bmatrix}$.
For $B = \begin{bmatrix} -1 & 2 & 1 \end{bmatrix}$, the transpose $B' = \begin{bmatrix} -1 \\ 2 \\ 1 \end{bmatrix}$.
We now compute the product of $B' (3 \times 1)$ and $A' (1 \times 3)$:
$B'A' = \begin{bmatrix} -1 \\ 2 \\ 1 \end{bmatrix} \begin{bmatrix} 1 & -4 & 3 \end{bmatrix} = \begin{bmatrix} (-1)(1) & (-1)(-4) & (-1)(3) \\ (2)(1) & (2)(-4) & (2)(3) \\ (1)(1) & (1)(-4) & (1)(3) \end{bmatrix}$
$B'A' = \begin{bmatrix} -1 & 4 & -3 \\ 2 & -8 & 6 \\ 1 & -4 & 3 \end{bmatrix}$
| Expression | Result |
|---|---|
| $(AB)'$ | $\begin{bmatrix} -1 & 4 & -3 \\ 2 & -8 & 6 \\ 1 & -4 & 3 \end{bmatrix}$ |
| $B'A'$ | $\begin{bmatrix} -1 & 4 & -3 \\ 2 & -8 & 6 \\ 1 & -4 & 3 \end{bmatrix}$ |
Comparing the matrices from Step 3 and Step 5, we observe that $(AB)' = B'A'$.
Final Solution: The property $(AB)' = B'A'$ is verified as both sides yield the matrix $\begin{bmatrix} -1 & 4 & -3 \\ 2 & -8 & 6 \\ 1 & -4 & 3 \end{bmatrix}$.
Solution:
Given the matrix $A = \begin{bmatrix} \cos \alpha & \sin \alpha \\ -\sin \alpha & \cos \alpha \end{bmatrix}$, the transpose matrix $A'$ is obtained by interchanging the rows and columns [Definition of Transpose].
$A' = \begin{bmatrix} \cos \alpha & -\sin \alpha \\ \sin \alpha & \cos \alpha \end{bmatrix}$
We perform the matrix multiplication $A'A$ using the row-by-column method [Matrix Multiplication Rule: $(AB)_{ij} = \sum_{k=1}^{n} a_{ik}b_{kj}$].
$A'A = \begin{bmatrix} \cos \alpha & -\sin \alpha \\ \sin \alpha & \cos \alpha \end{bmatrix} \begin{bmatrix} \cos \alpha & \sin \alpha \\ -\sin \alpha & \cos \alpha \end{bmatrix}$
We compute each element of the resulting $2 \times 2$ matrix:
Utilizing the Pythagorean identity $\sin^2 \theta + \cos^2 \theta = 1$ and the property of additive inverses:
| $\cos^2 \alpha + \sin^2 \alpha = 1$ | $\cos \alpha \sin \alpha - \sin \alpha \cos \alpha = 0$ |
| $\sin \alpha \cos \alpha - \cos \alpha \sin \alpha = 0$ | $\sin^2 \alpha + \cos^2 \alpha = 1$ |
Substituting the computed values back into the matrix structure:
$A'A = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}$
Since $\begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}$ is the Identity matrix of order 2, denoted as $I$ [Definition of Identity Matrix].
Final Solution: $A'A = I$ is verified.
Solution:
Any square matrix $A$ can be uniquely expressed as the sum of a symmetric matrix ($P$) and a skew-symmetric matrix ($Q$) using the following theorem:
$A = P + Q = \frac{1}{2}(A + A^T) + \frac{1}{2}(A - A^T)$
Where:
Given the matrix $A$:
$A = \begin{bmatrix} 1 & 5 \\ -1 & 2 \end{bmatrix}$
The transpose $A^T$ is obtained by interchanging rows and columns:
$A^T = \begin{bmatrix} 1 & -1 \\ 5 & 2 \end{bmatrix}$
$P = \frac{1}{2}(A + A^T) = \frac{1}{2} \left( \begin{bmatrix} 1 & 5 \\ -1 & 2 \end{bmatrix} + \begin{bmatrix} 1 & -1 \\ 5 & 2 \end{bmatrix} \right)$
$P = \frac{1}{2} \begin{bmatrix} 1+1 & 5-1 \\ -1+5 & 2+2 \end{bmatrix} = \frac{1}{2} \begin{bmatrix} 2 & 4 \\ 4 & 4 \end{bmatrix}$
$P = \begin{bmatrix} 1 & 2 \\ 2 & 2 \end{bmatrix}$
$Q = \frac{1}{2}(A - A^T) = \frac{1}{2} \left( \begin{bmatrix} 1 & 5 \\ -1 & 2 \end{bmatrix} - \begin{bmatrix} 1 & -1 \\ 5 & 2 \end{bmatrix} \right)$
$Q = \frac{1}{2} \begin{bmatrix} 1-1 & 5-(-1) \\ -1-5 & 2-2 \end{bmatrix} = \frac{1}{2} \begin{bmatrix} 0 & 6 \\ -6 & 0 \end{bmatrix}$
$Q = \begin{bmatrix} 0 & 3 \\ -3 & 0 \end{bmatrix}$
To verify, we perform the addition $P + Q$:
$\begin{bmatrix} 1 & 2 \\ 2 & 2 \end{bmatrix} + \begin{bmatrix} 0 & 3 \\ -3 & 0 \end{bmatrix} = \begin{bmatrix} 1+0 & 2+3 \\ 2-3 & 2+0 \end{bmatrix} = \begin{bmatrix} 1 & 5 \\ -1 & 2 \end{bmatrix} = A$
Final Solution: The matrix $\begin{bmatrix} 1 & 5 \\ -1 & 2 \end{bmatrix}$ is expressed as the sum of a symmetric and skew-symmetric matrix as $\begin{bmatrix} 1 & 2 \\ 2 & 2 \end{bmatrix} + \begin{bmatrix} 0 & 3 \\ -3 & 0 \end{bmatrix}$.
Solution:
Given that $A$ and $B$ are symmetric matrices of the same order $n \times n$, by definition, their transposes are equal to the matrices themselves:
We are required to determine the nature of the matrix $C$, defined as:
$C = AB - BA$
To classify the matrix $C$, we evaluate its transpose $C^T$ using the properties of matrix transpose operations:
$C^T = (AB - BA)^T$
Applying the linearity property of transposes, $(X - Y)^T = X^T - Y^T$ [Property of Transpose]:
$C^T = (AB)^T - (BA)^T$
Applying the reversal law of transposes, $(AB)^T = B^T A^T$ [Property of Transpose]:
$C^T = B^T A^T - A^T B^T$
Substitute the symmetry conditions ($A^T = A$ and $B^T = B$) into the expression:
$C^T = (B)(A) - (A)(B)$
$C^T = BA - AB$
Factor out the negative sign to relate it back to the original matrix $C$:
$C^T = -(AB - BA)$
$C^T = -C$
By definition, a matrix $M$ is skew-symmetric if $M^T = -M$ [Definition of Skew-Symmetric Matrix]. Since we have demonstrated that $(AB - BA)^T = -(AB - BA)$, the matrix $AB - BA$ satisfies the criteria for a skew-symmetric matrix.
Final Solution: The matrix $AB – BA$ is a skew-symmetric matrix.
Solution:
Given matrices:
$A = \begin{bmatrix} 0 \\ 1 \\ 2 \end{bmatrix}$ (Order: $3 \times 1$)
$B = \begin{bmatrix} 1 & 5 & 7 \end{bmatrix}$ (Order: $1 \times 3$)
To verify the property $(AB)' = B'A'$, we must perform matrix multiplication and transposition [Per the definition of Matrix Transposition and Matrix Product].
The product $AB$ of a $(3 \times 1)$ matrix and a $(1 \times 3)$ matrix results in a $(3 \times 3)$ matrix.
$AB = \begin{bmatrix} 0 \\ 1 \\ 2 \end{bmatrix} \times \begin{bmatrix} 1 & 5 & 7 \end{bmatrix}$
$AB = \begin{bmatrix} (0)(1) & (0)(5) & (0)(7) \\ (1)(1) & (1)(5) & (1)(7) \\ (2)(1) & (2)(5) & (2)(7) \end{bmatrix} = \begin{bmatrix} 0 & 0 & 0 \\ 1 & 5 & 7 \\ 2 & 10 & 14 \end{bmatrix}$
To find the transpose $(AB)'$, swap rows and columns [Per the property $A'_{ij} = A_{ji}$].
$(AB)' = \begin{bmatrix} 0 & 1 & 2 \\ 0 & 5 & 10 \\ 0 & 7 & 14 \end{bmatrix}$
$B' = \begin{bmatrix} 1 \\ 5 \\ 7 \end{bmatrix}$ (Order: $3 \times 1$)
$A' = \begin{bmatrix} 0 & 1 & 2 \end{bmatrix}$ (Order: $1 \times 3$)
The product $B'A'$ is a $(3 \times 1)$ matrix multiplied by a $(1 \times 3)$ matrix, resulting in a $(3 \times 3)$ matrix.
$B'A' = \begin{bmatrix} 1 \\ 5 \\ 7 \end{bmatrix} \times \begin{bmatrix} 0 & 1 & 2 \end{bmatrix}$
$B'A' = \begin{bmatrix} (1)(0) & (1)(1) & (1)(2) \\ (5)(0) & (5)(1) & (5)(2) \\ (7)(0) & (7)(1) & (7)(2) \end{bmatrix} = \begin{bmatrix} 0 & 1 & 2 \\ 0 & 5 & 10 \\ 0 & 7 & 14 \end{bmatrix}$
Comparing the results from Step 3 and Step 5:
| Expression | Resultant Matrix |
|---|---|
| $(AB)'$ | $\begin{bmatrix} 0 & 1 & 2 \\ 0 & 5 & 10 \\ 0 & 7 & 14 \end{bmatrix}$ |
| $B'A'$ | $\begin{bmatrix} 0 & 1 & 2 \\ 0 & 5 & 10 \\ 0 & 7 & 14 \end{bmatrix}$ |
Final Solution: Since $(AB)' = \begin{bmatrix} 0 & 1 & 2 \\ 0 & 5 & 10 \\ 0 & 7 & 14 \end{bmatrix}$ and $B'A' = \begin{bmatrix} 0 & 1 & 2 \\ 0 & 5 & 10 \\ 0 & 7 & 14 \end{bmatrix}$, it is verified that $(AB)' = B'A'$.
Solution:
Given the matrix $A = \begin{bmatrix} \cos \alpha & -\sin \alpha \\ \sin \alpha & \cos \alpha \end{bmatrix}$, the transpose $A'$ is obtained by interchanging the rows and columns [Definition of Transpose Matrix].
$A' = \begin{bmatrix} \cos \alpha & \sin \alpha \\ -\sin \alpha & \cos \alpha \end{bmatrix}$
Calculate the sum $A + A'$ by adding corresponding elements [Addition of Matrices Rule]:
$A + A' = \begin{bmatrix} \cos \alpha + \cos \alpha & -\sin \alpha + \sin \alpha \\ \sin \alpha - \sin \alpha & \cos \alpha + \cos \alpha \end{bmatrix}$
$A + A' = \begin{bmatrix} 2\cos \alpha & 0 \\ 0 & 2\cos \alpha \end{bmatrix}$
The problem states $A + A' = I$, where $I$ is the identity matrix of order 2, $I = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}$.
$\begin{bmatrix} 2\cos \alpha & 0 \\ 0 & 2\cos \alpha \end{bmatrix} = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}$
By comparing corresponding elements [Equality of Matrices Principle]:
$2\cos \alpha = 1$
$\cos \alpha = \frac{1}{2}$
Since $\cos \alpha = \cos(\frac{\pi}{3})$, the general solution is $\alpha = 2n\pi \pm \frac{\pi}{3}$ for $n \in \mathbb{Z}$. Within the principal domain, $\alpha = \frac{\pi}{3}$.
Final Solution: The value of $\alpha$ is $\frac{\pi}{3}$ (or generally $2n\pi \pm \frac{\pi}{3}$).
Solution:
Given matrices:
$A = \begin{bmatrix} -1 & 2 & 3 \\ 5 & 7 & 9 \\ -2 & 1 & 1 \end{bmatrix}$, $B = \begin{bmatrix} -4 & 1 & -5 \\ 1 & 2 & 0 \\ 1 & 3 & 1 \end{bmatrix}$
To compute the sum $A + B$, we add corresponding elements [Per the definition of Matrix Addition]:
$A + B = \begin{bmatrix} (-1 - 4) & (2 + 1) & (3 - 5) \\ (5 + 1) & (7 + 2) & (9 + 0) \\ (-2 + 1) & (1 + 3) & (1 + 1) \end{bmatrix} = \begin{bmatrix} -5 & 3 & -2 \\ 6 & 9 & 9 \\ -1 & 4 & 2 \end{bmatrix}$The transpose of a matrix is obtained by interchanging its rows and columns [Per the property $(A^T)_{ij} = A_{ji}$].
$(A + B)' = \begin{bmatrix} -5 & 6 & -1 \\ 3 & 9 & 4 \\ -2 & 9 & 2 \end{bmatrix}$Transposing matrix $A$:
$A' = \begin{bmatrix} -1 & 5 & -2 \\ 2 & 7 & 1 \\ 3 & 9 & 1 \end{bmatrix}$Transposing matrix $B$:
$B' = \begin{bmatrix} -4 & 1 & 1 \\ 1 & 2 & 3 \\ -5 & 0 & 1 \end{bmatrix}$| Left Hand Side $(A+B)'$ | Right Hand Side $A' + B'$ |
|---|---|
| $\begin{bmatrix} -5 & 6 & -1 \\ 3 & 9 & 4 \\ -2 & 9 & 2 \end{bmatrix}$ | $\begin{bmatrix} -5 & 6 & -1 \\ 3 & 9 & 4 \\ -2 & 9 & 2 \end{bmatrix}$ |
Since the resulting matrix from the Left Hand Side is identical to the matrix from the Right Hand Side, the property $(A + B)' = A' + B'$ is verified.
Final Solution: The identity $(A + B)' = A' + B'$ is verified as both sides yield $\begin{bmatrix} -5 & 6 & -1 \\ 3 & 9 & 4 \\ -2 & 9 & 2 \end{bmatrix}$.