2. Let G = GL(2, R). Prove that the following two subsets of GL(2, R) are subgroups of GL(2, R). (a) -{(82) A = d>0} a> 0 and d >

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I need help on 2a
1.
Let K be a subgroup of R*. Let H = {g E GL(n, R): det (g) E K}. Prove that H is a
subgroup of GL(n, R).
2.
Let G = GL(2, R). Prove that the following two subsets of GL(2, R) are subgroups of
GL(2, R).
(a)
(b)
3.
{(82)
b
= {(1 i): bER}
A =
N =
Here's a trickier example of a subgroup of GL(2, R):
cos 6-sin)} {(
sin
= {(²
K =
: a>0 and d
and d
d>0}
>
>
0 5
3 -12
cos o
sin o
sin o
>)}
- cos p
Prove that K is indeed a subgroup of GL(2, R).
(You will probably recognize the elements of K from an earlier homework.)
4.
There is a theorem that says that every element g E GL(2, R) can be written, in a
unique way, as kan for some k EK, a E A, and n E N (with K, A, N as in the last two
problems). Your job:
(a)
If g =
find k, a, n, such that g = kan.
-3 -17
(b)
If g = √(3 find k, a, n, such that g =
7
kan.
For both of these, show your work and explain how
you
found your answers.
Helpful fact: if det g> 0, then k will be a rotation, and if det g < 0, then k will be a
reflection.
Transcribed Image Text:1. Let K be a subgroup of R*. Let H = {g E GL(n, R): det (g) E K}. Prove that H is a subgroup of GL(n, R). 2. Let G = GL(2, R). Prove that the following two subsets of GL(2, R) are subgroups of GL(2, R). (a) (b) 3. {(82) b = {(1 i): bER} A = N = Here's a trickier example of a subgroup of GL(2, R): cos 6-sin)} {( sin = {(² K = : a>0 and d and d d>0} > > 0 5 3 -12 cos o sin o sin o >)} - cos p Prove that K is indeed a subgroup of GL(2, R). (You will probably recognize the elements of K from an earlier homework.) 4. There is a theorem that says that every element g E GL(2, R) can be written, in a unique way, as kan for some k EK, a E A, and n E N (with K, A, N as in the last two problems). Your job: (a) If g = find k, a, n, such that g = kan. -3 -17 (b) If g = √(3 find k, a, n, such that g = 7 kan. For both of these, show your work and explain how you found your answers. Helpful fact: if det g> 0, then k will be a rotation, and if det g < 0, then k will be a reflection.
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