# MIT-exam-eye-catch

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• Determine whether the Given 3 by 3 Matrices are Nonsingular Determine whether the following matrices are nonsingular or not. (a) $A=\begin{bmatrix} 1 & 0 & 1 \\ 2 &1 &2 \\ 1 & 0 & -1 \end{bmatrix}$. (b) $B=\begin{bmatrix} 2 & 1 & 2 \\ 1 &0 &1 \\ 4 & 1 & 4 \end{bmatrix}$.   Solution. Recall that […]
• Normalize Lengths to Obtain an Orthonormal Basis Let $\mathbf{v}_{1} = \begin{bmatrix} 1 \\ 1 \end{bmatrix} ,\; \mathbf{v}_{2} = \begin{bmatrix} 1 \\ -1 \end{bmatrix} .$ Let $V=\Span(\mathbf{v}_{1},\mathbf{v}_{2})$. Do $\mathbf{v}_{1}$ and $\mathbf{v}_{2}$ form an orthonormal basis for $V$? If […]
• Automorphism Group of $\Q(\sqrt[3]{2})$ Over $\Q$. Determine the automorphism group of $\Q(\sqrt[3]{2})$ over $\Q$. Proof. Let $\sigma \in \Aut(\Q(\sqrt[3]{2}/\Q)$ be an automorphism of $\Q(\sqrt[3]{2})$ over $\Q$. Then $\sigma$ is determined by the value $\sigma(\sqrt[3]{2})$ since any element $\alpha$ of $\Q(\sqrt[3]{2})$ […]
• Abelian Normal subgroup, Quotient Group, and Automorphism Group Let $G$ be a finite group and let $N$ be a normal abelian subgroup of $G$. Let $\Aut(N)$ be the group of automorphisms of $G$. Suppose that the orders of groups $G/N$ and $\Aut(N)$ are relatively prime. Then prove that $N$ is contained in the center of […]
• Find a Condition that a Vector be a Linear Combination Let $\mathbf{v}=\begin{bmatrix} a \\ b \\ c \end{bmatrix}, \qquad \mathbf{v}_1=\begin{bmatrix} 1 \\ 2 \\ 0 \end{bmatrix}, \qquad \mathbf{v}_2=\begin{bmatrix} 2 \\ -1 \\ 2 \end{bmatrix}.$ Find the necessary and […]
• Prove that $\{ 1 , 1 + x , (1 + x)^2 \}$ is a Basis for the Vector Space of Polynomials of Degree $2$ or Less Let $\mathbf{P}_2$ be the vector space of polynomials of degree $2$ or less. (a) Prove that the set $\{ 1 , 1 + x , (1 + x)^2 \}$ is a basis for $\mathbf{P}_2$. (b) Write the polynomial $f(x) = 2 + 3x - x^2$ as a linear combination of the basis $\{ 1 , 1+x , (1+x)^2 […] • Abelian Groups and Surjective Group Homomorphism Let$G, G'$be groups. Suppose that we have a surjective group homomorphism$f:G\to G'$. Show that if$G$is an abelian group, then so is$G'$. Definitions. Recall the relevant definitions. A group homomorphism$f:G\to G'$is a map from$G$to$G'$[…] • Two Normal Subgroups Intersecting Trivially Commute Each Other Let$G$be a group. Assume that$H$and$K$are both normal subgroups of$G$and$H \cap K=1$. Then for any elements$h \in H$and$k\in K$, show that$hk=kh$. Proof. It suffices to show that$h^{-1}k^{-1}hk \in H \cap K\$. In fact, if this it true then we have […]