Found problems: 36
Calculate the determinant of the $ n\times n $ complex matrix $ \left(a_j^i\right)_{1\le j\le n}^{1\le i\le n} $ defined by
$$ a_j^i=\left\{\begin{matrix} 1+x^2,\quad i=j\\x,\quad |i-j|=1\\0,\quad |i-j|\ge 2\end{matrix}\right. , $$
where $ n $ is a natural number greater than $ 2. $
Let $n \in \mathbb{N},n \ge 2,$ and $A,B \in \mathcal{M}_n(\mathbb{R}).$ Prove that there exists a complex number $z,$ such that $|z|=1$ and $$\Re \left( {\det(A+zB)} \right) \ge \det(A)+\det(B),$$ where $\Re(w)$ is the real part of the complex number $w.$
Let $n$ be a positive integer, and let $M_n$ be the set of invertible matrices with integer entries and size $n \times n$.
(a) Find the largest possible value of $n$ such that there exists a symmetric matrix $A \in M_n$ satisfying
\[
\det(A^{20} + A^{24}) < 2024.
\]
(b) Prove that for every $n$, there exists a matrix $B \in M_n$ such that
\[
\det(B^{20} + B^{24}) < 2024.
\]
Let $\mathcal{M}$ be the set of all $2021 \times 2021$ matrices with at most two entries in each row equal to $1$ and all other entries equal to $0$.
Determine the size of the set $\{ \det A : A \in M \}$.
[i]Here $\det A$ denotes the determinant of the matrix $A$.[/i]
Let be two matrices $ A,B\in M_2\left(\mathbb{R}\right) $ and two natural numbers $ m,n. $ Prove that:
$$ \det\left( (AB)^m-(BA)^m\right)\cdot\det\left( (AB)^n-(BA)^n\right)\ge 0. $$
Without calculating the value of the determinant
$$ \begin{vmatrix}1 &1 &3& 1\\1& 2& 3 &5\\ 3& 0& 5& 5\\ 0& a& -11a& a^{13}+9a\end{vmatrix} , $$
show that it is divisible by $ 26, $ for any integer $ a. $
Let $A=(\alpha_{ij})$ be a $m\,x\,n$ matric and $B=(\beta_{kl})$ be a $n\,x\, m$ matric with $m>n$ . Prove that $D(A\cdot B)=0$.
$A$ and $B$ are $2\times 2$ real valued matrices satisfying
$$\det A = \det B = 1,\quad \text{tr}(A)>2,\quad \text{tr}(B)>2,\quad \text{tr}(ABA^{-1}B^{-1}) = 2$$
Prove that $A$ and $B$ have a common eigenvector.
Let $D_n$ be the determinant of order $n$ of which the element in the $i$-th row and the $j$-th
column is $|i-j|.$ Show that $D_n$ is equal to
$$(-1)^{n-1}(n-1)2^{n-2}.$$
Prove that if $A{}$ and $B{}$ are $n\times n$ matrices with complex entries which satisfy \[A=AB-BA+A^2B-2ABA+BA^2+A^2BA-ABA^2,\]then $\det(A)=0$.
$n\geq 2$ is a given integer. For two permuations $(\alpha_1,\cdots,\alpha_n)$ and $(\beta_1,\cdots,\beta_n)$ of $1,\cdots,n$, consider $n\times n$ matrix $A= \left(a_{ij} \right)_{1\leq i,j\leq n}$ defined by $a_{ij} = (1+\alpha_i \beta_j )^{n-1}$. Find every possible value of $\det(A)$.
We consider a natural number $n$, $n \geq 2$ and the matrices
\begin{tabular}{cc}
$A= \begin{pmatrix} 1 & 2 & 3 & \cdots & n\\ n & 1 & 2 & \cdots & n - 1\\ n - 1 & n & 1 & \cdots & n - 2\\ \cdots & \cdots & \cdots & \cdots & \cdots\\2 & 3 & 4 & \cdots & 1 \end{pmatrix}$
\end{tabular}
Show that$$\epsilon^ndet\left(I_n-A^{2n}\right)+\epsilon^{n-1}det\left(\epsilon I_n-A^{2n}\right)+\epsilon^{n-2}det\left(\epsilon^2 I_n-A^{2n}\right)+\cdots +det\left(\epsilon^n I_n-A^{2n}\right)$$ $$=n(-1)^{n-1}\left[\frac{n^n(n+1)}{2}\right]^{2n^2-4n}\left(1+(n+1)^{2n}\left(2n+(-1)^n{{2n}\choose{n}}\right)\right)$$where $\epsilon \in \mathbb{C}\backslash \mathbb{R}$, $\epsilon^{n+1}=1$
Let $a$, $b$ and $c$ be complex numbers such that $abc = 1$. Find the value of the cubic root of
\begin{tabular}{|ccc|}
$b + n^3c$ & $n(c - b)$ & $n^2(b - c)$\\
$n^2(c - a)$ & $c + n^3a$ & $n(a - c)$\\
$n(b - a)$ & $n^2(a - b)$ & $a + n^3b$
\end{tabular}
Let $n$ be a nonzero natural number and $f:\mathbb R\to\mathbb R\setminus\{0\}$ be a function such that $f(2014)=1-f(2013)$. Let $x_1,x_2,x_3,\ldots,x_n$ be real numbers not equal to each other. If
$$\begin{vmatrix}1+f(x_1)&f(x_2)&f(x_3)&\cdots&f(x_n)\\f(x_1)&1+f(x_2)&f(x_3)&\cdots&f(x_n)\\f(x_1)&f(x_2)&1+f(x_3)&\cdots&f(x_n)\\\vdots&\vdots&\vdots&\ddots&\vdots\\f(x_1)&f(x_2)&f(x_3)&\cdots&1+f(x_n)\end{vmatrix}=0,$$prove that $f$ is not continuous.
$n(\geq 2)$ is a given integer and $T$ is set of all $n\times n$ matrices whose entries are elements of the set $S=\{1,\cdots,2017\}$. Evaluate the following value.
\[\sum_{A\in T} \text{det}(A)\]
Let $x_1, x_2, \dots, x_n$ be different real numbers. Prove that
\[\sum_{1 \leqslant i \leqslant n} \prod_{j \neq i} \frac{1-x_{i} x_{j}}{x_{i}-x_{j}}=\left\{\begin{array}{ll}
0, & \text { if } n \text { is even; } \\
1, & \text { if } n \text { is odd. }
\end{array}\right.\]
Let $n$ be an odd natural number and $A,B \in \mathcal{M}_n(\mathbb{C})$ be two matrices such that $(A-B)^2=O_n.$ Prove that $\det(AB-BA)=0.$
Show that for any natural numbers $ m,n\ge 3, $ the equation $ \Delta_n (x)=0 $ has exactly two distinct solutions, where
$$ \Delta_n (x)=\begin{vmatrix}1 & 1-m & 1-m & \cdots & 1-m & 1-m & -m \\ -1 & \binom{m}{x} & 0 & \cdots & 0 & 0 & 0 \\ 0 & -1 & \binom{m}{x} & \cdots & 0 & 0 & 0 \\ \cdots & \cdots & \cdots & \cdots & \cdots & \cdots & \cdots \\ 0 & 0 & 0 & \cdots & -1 & \binom{m}{x} & 0 \\ 0 & 0 & 0 & \cdots & 0 & -1 & \binom{m}{x}\end{vmatrix} . $$
Let $a,b, p_1 ,p_2, \ldots, p_n$ be real numbers with $a \ne b$. Define $f(x)= (p_1 -x) (p_2 -x) \cdots (p_n -x)$. Show that
$$ \text{det} \begin{pmatrix} p_1 & a& a & \cdots & a \\
b & p_2 & a & \cdots & a\\
b & b & p_3 & \cdots & a\\
\vdots & \vdots & \vdots & \ddots & \vdots\\
b & b& b &\cdots &p_n
\end{pmatrix}= \frac{bf(a) -af(b)}{b-a}.$$
Let $x_1, x_2, \dots, x_n$ be different real numbers. Prove that
\[\sum_{1 \leqslant i \leqslant n} \prod_{j \neq i} \frac{1-x_{i} x_{j}}{x_{i}-x_{j}}=\left\{\begin{array}{ll}
0, & \text { if } n \text { is even; } \\
1, & \text { if } n \text { is odd. }
\end{array}\right.\]
Given the determinant of order $n$
$$\begin{vmatrix}
8 & 3 & 3 & \dots & 3 \\
3 & 8 & 3 & \dots & 3 \\
3 & 3 & 8 & \dots & 3 \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
3 & 3 & 3 & \dots & 8
\end{vmatrix}$$
Calculate its value and determine for which values of $n$ this value is a multiple of $10$.
Let $x_1, x_2, \dots, x_n$ be different real numbers. Prove that
\[\sum_{1 \leqslant i \leqslant n} \prod_{j \neq i} \frac{1-x_{i} x_{j}}{x_{i}-x_{j}}=\left\{\begin{array}{ll}
0, & \text { if } n \text { is even; } \\
1, & \text { if } n \text { is odd. }
\end{array}\right.\]
Find the remainder upon division by $x^2-1$ of the determinant
$$\begin{vmatrix}
x^3+3x & 2 & 1 & 0
\\ x^2+5x & 3 & 0 & 2
\\x^4 +x^2+1 & 2 & 1 & 3
\\x^5 +1 & 1 & 2 & 3
\\ \end{vmatrix}$$
Let $D_n$ denote the value of the $(n -1) \times (n - 1)$ determinant
$$ \begin{pmatrix}
3 & 1 &1 & \ldots & 1\\
1 & 4 &1 & \ldots & 1\\
1 & 1 & 5 & \ldots & 1\\
\vdots & \vdots & \vdots & \ddots & \vdots\\
1 & 1 & 1 & \ldots & n+1
\end{pmatrix}.$$
Is the set $\left\{ \frac{D_n }{n!} \, | \, n \geq 2\right\}$ bounded?
For any $n\times n$ unitary matrices $A,B$, prove that $|\det (A+2B)|\leq 3^n$.