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  • Is the Following Function $T:\R^2 \to \R^3$ a Linear Transformation?Is the Following Function $T:\R^2 \to \R^3$ a Linear Transformation? Determine whether the function $T:\R^2 \to \R^3$ defined by \[T\left(\, \begin{bmatrix} x \\ y \end{bmatrix} \,\right) = \begin{bmatrix} x_+y \\ x+1 \\ 3y \end{bmatrix}\] is a linear transformation.   Solution. The […]
  • Dihedral Group and Rotation of the PlaneDihedral Group and Rotation of the Plane Let $n$ be a positive integer. Let $D_{2n}$ be the dihedral group of order $2n$. Using the generators and the relations, the dihedral group $D_{2n}$ is given by \[D_{2n}=\langle r,s \mid r^n=s^2=1, sr=r^{-1}s\rangle.\] Put $\theta=2 \pi/n$. (a) Prove that the matrix […]
  • Find the Rank of a Matrix with a ParameterFind the Rank of a Matrix with a Parameter Find the rank of the following real matrix. \[ \begin{bmatrix} a & 1 & 2 \\ 1 &1 &1 \\ -1 & 1 & 1-a \end{bmatrix},\] where $a$ is a real number.   (Kyoto University, Linear Algebra Exam) Solution. The rank is the number of nonzero rows of a […]
  • Find the Nullspace and Range of the Linear Transformation $T(f)(x) = f(x)-f(0)$Find the Nullspace and Range of the Linear Transformation $T(f)(x) = f(x)-f(0)$ Let $C([-1, 1])$ denote the vector space of real-valued functions on the interval $[-1, 1]$. Define the vector subspace \[W = \{ f \in C([-1, 1]) \mid f(0) = 0 \}.\] Define the map $T : C([-1, 1]) \rightarrow W$ by $T(f)(x) = f(x) - f(0)$. Determine if $T$ is a linear map. If […]
  • Linear Algebra Midterm 1 at the Ohio State University (2/3)Linear Algebra Midterm 1 at the Ohio State University (2/3) The following problems are Midterm 1 problems of Linear Algebra (Math 2568) at the Ohio State University in Autumn 2017. There were 9 problems that covered Chapter 1 of our textbook (Johnson, Riess, Arnold). The time limit was 55 minutes. This post is Part 2 and contains […]
  • If the Augmented Matrix is Row-Equivalent to the Identity Matrix, is the System Consistent?If the Augmented Matrix is Row-Equivalent to the Identity Matrix, is the System Consistent? Consider the following system of linear equations: \begin{align*} ax_1+bx_2 &=c\\ dx_1+ex_2 &=f\\ gx_1+hx_2 &=i. \end{align*} (a) Write down the augmented matrix. (b) Suppose that the augmented matrix is row equivalent to the identity matrix. Is the system consistent? […]
  • The Inverse Matrix of an Upper Triangular Matrix with VariablesThe Inverse Matrix of an Upper Triangular Matrix with Variables Let $A$ be the following $3\times 3$ upper triangular matrix. \[A=\begin{bmatrix} 1 & x & y \\ 0 &1 &z \\ 0 & 0 & 1 \end{bmatrix},\] where $x, y, z$ are some real numbers. Determine whether the matrix $A$ is invertible or not. If it is invertible, then find […]
  • If a Power of a Matrix is the Identity, then the Matrix is DiagonalizableIf a Power of a Matrix is the Identity, then the Matrix is Diagonalizable Let $A$ be an $n \times n$ complex matrix such that $A^k=I$, where $I$ is the $n \times n$ identity matrix. Show that the matrix $A$ is diagonalizable. Hint. Use the fact that if the minimal polynomial for the matrix $A$ has distinct roots, then $A$ is […]

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