Let
\[
A=
\begin{bmatrix}
8 & 1 & 6 \\
3 & 5 & 7 \\
4 & 9 & 2
\end{bmatrix}
.
\]
Notice that $A$ contains every integer from $1$ to $9$ and that the sums of each row, column, and diagonal of $A$ are equal. Such a grid is sometimes called a magic square.

Find Inverse Matrices Using Adjoint Matrices
Let $A$ be an $n\times n$ matrix.
The $(i, j)$ cofactor $C_{ij}$ of $A$ is defined to be
\[C_{ij}=(-1)^{ij}\det(M_{ij}),\]
where $M_{ij}$ is the $(i,j)$ minor matrix obtained from $A$ removing the $i$-th row and $j$-th column.
Then consider the $n\times n$ matrix […]

Determine Whether There Exists a Nonsingular Matrix Satisfying $A^4=ABA^2+2A^3$
Determine whether there exists a nonsingular matrix $A$ if
\[A^4=ABA^2+2A^3,\]
where $B$ is the following matrix.
\[B=\begin{bmatrix}
-1 & 1 & -1 \\
0 &-1 &0 \\
2 & 1 & -4
\end{bmatrix}.\]
If such a nonsingular matrix $A$ exists, find the inverse […]

Find All Values of $x$ such that the Matrix is Invertible
Given any constants $a,b,c$ where $a\neq 0$, find all values of $x$ such that the matrix $A$ is invertible if
\[
A=
\begin{bmatrix}
1 & 0 & c \\
0 & a & -b \\
-1/a & x & x^{2}
\end{bmatrix}
.
\]
Solution.
We know that $A$ is invertible precisely when […]

How to Use the Cayley-Hamilton Theorem to Find the Inverse Matrix
Find the inverse matrix of the $3\times 3$ matrix
\[A=\begin{bmatrix}
7 & 2 & -2 \\
-6 &-1 &2 \\
6 & 2 & -1
\end{bmatrix}\]
using the Cayley-Hamilton theorem.
Solution.
To apply the Cayley-Hamilton theorem, we first determine the characteristic […]

Find the Inverse Matrix Using the Cayley-Hamilton Theorem Find the inverse matrix of the matrix
\[A=\begin{bmatrix}
1 & 1 & 2 \\
9 &2 &0 \\
5 & 0 & 3
\end{bmatrix}\]
using the Cayley–Hamilton theorem.
Solution.
To use the Cayley-Hamilton theorem, we first compute the characteristic polynomial $p(t)$ of […]

Quiz 11. Find Eigenvalues and Eigenvectors/ Properties of Determinants
(a) Find all the eigenvalues and eigenvectors of the matrix
\[A=\begin{bmatrix}
3 & -2\\
6& -4
\end{bmatrix}.\]
(b) Let
\[A=\begin{bmatrix}
1 & 0 & 3 \\
4 &5 &6 \\
7 & 0 & 9
\end{bmatrix} \text{ and } B=\begin{bmatrix}
2 & 0 & 0 \\
0 & 3 &0 […]

Compute Determinant of a Matrix Using Linearly Independent Vectors
Let $A$ be a $3 \times 3$ matrix.
Let $\mathbf{x}, \mathbf{y}, \mathbf{z}$ are linearly independent $3$-dimensional vectors. Suppose that we have
\[A\mathbf{x}=\begin{bmatrix}
1 \\
0 \\
1
\end{bmatrix}, A\mathbf{y}=\begin{bmatrix}
0 \\
1 \\
0
[…]

Use Cramer’s Rule to Solve a $2\times 2$ System of Linear Equations
Use Cramer's rule to solve the system of linear equations
\begin{align*}
3x_1-2x_2&=5\\
7x_1+4x_2&=-1.
\end{align*}
Solution.
Let
\[A=[A_1, A_2]=\begin{bmatrix}
3 & -2\\
7& 4
\end{bmatrix},\]
be the coefficient matrix of the system, where $A_1, A_2$ […]

Define two functions $T:\R^{2}\to\R^{2}$ and $S:\R^{2}\to\R^{2}$ by \[ T\left( \begin{bmatrix} x \\ y \end{bmatrix} \right) = \begin{bmatrix} 2x+y \\ 0...