# number2018

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• Find the Eigenvalues and Eigenvectors of the Matrix $A^4-3A^3+3A^2-2A+8E$. Let $A=\begin{bmatrix} 1 & -1\\ 2& 3 \end{bmatrix}.$ Find the eigenvalues and the eigenvectors of the matrix $B=A^4-3A^3+3A^2-2A+8E.$ (Nagoya University Linear Algebra Exam Problem)   Hint. Apply the Cayley-Hamilton theorem. That is if $p_A(t)$ is the […]
• The Transpose of a Nonsingular Matrix is Nonsingular Let $A$ be an $n\times n$ nonsingular matrix. Prove that the transpose matrix $A^{\trans}$ is also nonsingular.   Definition (Nonsingular Matrix). By definition, $A^{\trans}$ is a nonsingular matrix if the only solution to […]
• Is an Eigenvector of a Matrix an Eigenvector of its Inverse? Suppose that $A$ is an $n \times n$ matrix with eigenvalue $\lambda$ and corresponding eigenvector $\mathbf{v}$. (a) If $A$ is invertible, is $\mathbf{v}$ an eigenvector of $A^{-1}$? If so, what is the corresponding eigenvalue? If not, explain why not. (b) Is $3\mathbf{v}$ an […]
• Diagonalize the Upper Triangular Matrix and Find the Power of the Matrix Consider the $2\times 2$ complex matrix $A=\begin{bmatrix} a & b-a\\ 0& b \end{bmatrix}.$ (a) Find the eigenvalues of $A$. (b) For each eigenvalue of $A$, determine the eigenvectors. (c) Diagonalize the matrix $A$. (d) Using the result of the […]
• Explicit Field Isomorphism of Finite Fields (a) Let $f_1(x)$ and $f_2(x)$ be irreducible polynomials over a finite field $\F_p$, where $p$ is a prime number. Suppose that $f_1(x)$ and $f_2(x)$ have the same degrees. Then show that fields $\F_p[x]/(f_1(x))$ and $\F_p[x]/(f_2(x))$ are isomorphic. (b) Show that the polynomials […]
• Vector Space of Polynomials and a Basis of Its Subspace Let $P_2$ be the vector space of all polynomials of degree two or less. Consider the subset in $P_2$ $Q=\{ p_1(x), p_2(x), p_3(x), p_4(x)\},$ where \begin{align*} &p_1(x)=1, &p_2(x)=x^2+x+1, \\ &p_3(x)=2x^2, &p_4(x)=x^2-x+1. \end{align*} (a) Use the basis $B=\{1, x, […] • Rank and Nullity of Linear Transformation From$\R^3$to$\R^2$Let$T:\R^3 \to \R^2$be a linear transformation such that $T(\mathbf{e}_1)=\begin{bmatrix} 1 \\ 0 \end{bmatrix}, T(\mathbf{e}_2)=\begin{bmatrix} 0 \\ 1 \end{bmatrix}, T(\mathbf{e}_3)=\begin{bmatrix} 1 \\ 0 \end{bmatrix},$ where$\mathbf{e}_1, […]
• A Condition that a Linear System has Nontrivial Solutions For what value(s) of $a$ does the system have nontrivial solutions? \begin{align*} &x_1+2x_2+x_3=0\\ &-x_1-x_2+x_3=0\\ & 3x_1+4x_2+ax_3=0. \end{align*}   Solution. First note that the system is homogeneous and hence it is consistent. Thus if the system has a nontrivial […]