2. Let G = GL(2, R). Prove that the following two subsets of GL(2, R) are subgroups of GL(2, R). (a) (b) {(89) b = {(1 1): DER} A = N = d>0} : a>0 and d >

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## Problem Statement

2. Let \( G = GL(2, \mathbb{R}) \). Prove that the following two subsets of \( GL(2, \mathbb{R}) \) are subgroups of \( GL(2, \mathbb{R}) \).

### (a)
\[ 
A = \left\{ 
\begin{pmatrix} 
a & 0 \\ 
0 & d 
\end{pmatrix} 
: a > 0 \text{ and } d > 0 
\right\} 
\]

### (b)
\[ 
N = \left\{ 
\begin{pmatrix} 
1 & b \\ 
0 & 1 
\end{pmatrix} 
: b \in \mathbb{R} 
\right\} 
\]

3. Here’s a trickier example of a subgroup of \( GL(2, \mathbb{R}) \):

\[ 
K = \left\{ 
\begin{pmatrix} 
\cos \theta & -\sin \theta \\ 
\sin \theta & \cos \theta 
\end{pmatrix} 
\right\} 
\cup 
\left\{ 
\begin{pmatrix} 
\cos \phi & \sin \phi \\ 
\sin \phi & -\cos \phi 
\end{pmatrix} 
\right\} 
\]

Prove that \( K \) is indeed a subgroup of \( GL(2, \mathbb{R}) \).
(You will probably recognize the elements of \( K \) from an earlier homework.)

4. There is a theorem that says that every element \( g \in GL(2, \mathbb{R}) \) can be written, in a unique way, as \( kan \) for some \( k \in K \), \( a \in A \), and \( n \in N \) (with \( K, A, N \) as in the last two problems). Your job:

### (a)
If \( g = 
\begin{pmatrix} 
0 & 5 \\ 
3 & -12 
\end{pmatrix} 
\), find \( k, a, n \), such that \( g = kan \).

### (b)
If \( g = 
\begin{pmatrix} 
-3 & -
Transcribed Image Text:## Problem Statement 2. Let \( G = GL(2, \mathbb{R}) \). Prove that the following two subsets of \( GL(2, \mathbb{R}) \) are subgroups of \( GL(2, \mathbb{R}) \). ### (a) \[ A = \left\{ \begin{pmatrix} a & 0 \\ 0 & d \end{pmatrix} : a > 0 \text{ and } d > 0 \right\} \] ### (b) \[ N = \left\{ \begin{pmatrix} 1 & b \\ 0 & 1 \end{pmatrix} : b \in \mathbb{R} \right\} \] 3. Here’s a trickier example of a subgroup of \( GL(2, \mathbb{R}) \): \[ K = \left\{ \begin{pmatrix} \cos \theta & -\sin \theta \\ \sin \theta & \cos \theta \end{pmatrix} \right\} \cup \left\{ \begin{pmatrix} \cos \phi & \sin \phi \\ \sin \phi & -\cos \phi \end{pmatrix} \right\} \] Prove that \( K \) is indeed a subgroup of \( GL(2, \mathbb{R}) \). (You will probably recognize the elements of \( K \) from an earlier homework.) 4. There is a theorem that says that every element \( g \in GL(2, \mathbb{R}) \) can be written, in a unique way, as \( kan \) for some \( k \in K \), \( a \in A \), and \( n \in N \) (with \( K, A, N \) as in the last two problems). Your job: ### (a) If \( g = \begin{pmatrix} 0 & 5 \\ 3 & -12 \end{pmatrix} \), find \( k, a, n \), such that \( g = kan \). ### (b) If \( g = \begin{pmatrix} -3 & -
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