# Math-Magic Tree example

• The Trick of a Mathematical Game. The One’s Digit of the Sum of Two Numbers. Decipher the trick of the following mathematical magic.   The Rule of the Game Here is the game. Pick six natural numbers ($1, 2, 3, \dots$) and place them in the yellow discs of the picture below. For example, let's say I have chose the numbers $7, 5, 3, 2, […] • Linear Algebra Midterm 1 at the Ohio State University (3/3) The following problems are Midterm 1 problems of Linear Algebra (Math 2568) at the Ohio State University in Autumn 2017. There were 9 problems that covered Chapter 1 of our textbook (Johnson, Riess, Arnold). The time limit was 55 minutes. This post is Part 3 and contains […] • Matrices Satisfying$HF-FH=-2F$Let$F$and$H$be an$n\times n$matrices satisfying the relation $HF-FH=-2F.$ (a) Find the trace of the matrix$F$. (b) Let$\lambda$be an eigenvalue of$H$and let$\mathbf{v}$be an eigenvector corresponding to$\lambda$. Show that there exists an positive integer$N$[…] • If Two Vectors Satisfy$A\mathbf{x}=0$then Find Another Solution Suppose that the vectors $\mathbf{v}_1=\begin{bmatrix} -2 \\ 1 \\ 0 \\ 0 \\ 0 \end{bmatrix}, \qquad \mathbf{v}_2=\begin{bmatrix} -4 \\ 0 \\ -3 \\ -2 \\ 1 \end{bmatrix}$ are a basis vectors for the null space of a$4\times 5$[…] • The Preimage of a Normal Subgroup Under a Group Homomorphism is Normal Let$G$and$G'$be groups and let$f:G \to G'$be a group homomorphism. If$H'$is a normal subgroup of the group$G'$, then show that$H=f^{-1}(H')$is a normal subgroup of the group$G$. Proof. We prove that$H$is normal in$G$. (The fact that$H$is a subgroup […] • Determinant of Matrix whose Diagonal Entries are 6 and 2 Elsewhere Find the determinant of the following matrix $A=\begin{bmatrix} 6 & 2 & 2 & 2 &2 \\ 2 & 6 & 2 & 2 & 2 \\ 2 & 2 & 6 & 2 & 2 \\ 2 & 2 & 2 & 6 & 2 \\ 2 & 2 & 2 & 2 & 6 \end{bmatrix}.$ (Harvard University, Linear Algebra Exam […] • Is the Set of All Orthogonal Matrices a Vector Space? An$n\times n$matrix$A$is called orthogonal if$A^{\trans}A=I$. Let$V$be the vector space of all real$2\times 2$matrices. Consider the subset $W:=\{A\in V \mid \text{A is an orthogonal matrix}\}.$ Prove or disprove that$W\$ is a subspace of […]