*aa3.2 Let Q be the group of rational numbers under addition

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Discussion Overview

The discussion revolves around the groups of rational numbers under addition and nonzero rational numbers under multiplication, specifically focusing on the elements generated by the fraction $\frac{1}{2}$ in both groups. Participants explore the implications of these groups and the concept of the order of elements.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant lists the elements in $\langle\frac{1}{2}\rangle$ in $Q$ as $\left\{\frac{n}{2} \vert n \in \mathbb{Z}\right\}$, indicating a set of rational numbers generated by $\frac{1}{2}$ through addition.
  • Another participant confirms the previous claim about $\langle\frac{1}{2}\rangle$ in $Q$ and asks for the corresponding elements in $\mathbb{Q}^*$.
  • In $\mathbb{Q}^*$, one participant proposes that $\langle\frac{1}{2}\rangle = \left\{2^n \vert n \in \mathbb{Z}\right\}$, representing the powers of 2 generated by $\frac{1}{2}$ through multiplication.
  • Participants discuss the concept of the order of elements, questioning how many times an element must be added or multiplied to reach the identity element in each group.
  • There is a clarification about the order of an element, emphasizing that it refers to the number of operations needed to reach the identity element, with specific examples provided for both $Q$ and $Q^*$.

Areas of Agreement / Disagreement

Participants generally agree on the definitions and properties of the groups and the elements generated by $\frac{1}{2}$, but the discussion about the order of elements remains somewhat unresolved, with different interpretations being explored.

Contextual Notes

Some participants express uncertainty about the order of elements, particularly in relation to how many times an element must be added or multiplied to reach the identity element, indicating a need for further clarification.

karush
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aa3.2

Let Q be the group of rational numbers under addition
and let $Q^∗$ be the group of
nonzero rational numbers under multiplication.
In $Q$, list the elements in $\langle\frac{1}{2} \rangle$,
In ${Q^∗}$ list elements in $\langle\frac{1}{2}\rangle $

ok just had time to post and clueless
 
Last edited:
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Hi karush,

Can you provide some attempt, or at least some initial thoughts please?
 
I like Serena said:
Hi karush,

Can you provide some attempt, or at least some initial thoughts please?
In Q,
$\langle\frac{1}{2}\rangle
=\left\{\cdots,-2,-\frac{3}{2},-1,-\frac{1}{2},
0,\frac{1}{2},1,\frac{3}{2},2\cdots\right\}
=\left\{\frac{n}{2}\vert n \in \Bbb{Z}\right\}$
 
karush said:
In Q,
$\langle\frac{1}{2}\rangle
=\left\{\cdots,-2,-\frac{3}{2},-1,-\frac{1}{2},
0,\frac{1}{2},1,\frac{3}{2},2\cdots\right\}
=\left\{\frac{n}{2}\vert n \in \Bbb{Z}\right\}$

Yep. That is correct. (Nod)

How did you find it?
Can you also find $\langle\frac{1}{2}\rangle$ in $\mathbb Q^*$?
 
I like Serena said:
Yep. That is correct. (Nod)

How did you find it?
Can you also find $\langle\frac{1}{2}\rangle$ in $\mathbb Q^*$?
In $Q*$
$\langle\frac{1}{2}\rangle
=\left\{\cdots, 4,2,1,\frac{1}{2},\frac{1}{4}, \cdots\right\}
=\left\{2^n\vert n \in \Bbb{Z}\right\}$
sorta!

$Q$ and $Q^\ast$ as above.
Find the order of each element in $Q$ and $Q^\ast$

ok is this like $4=2^2$
 
Last edited:
karush said:
In $Q*$
$\langle\frac{1}{2}\rangle
=\left\{\cdots, 4,2,1,\frac{1}{2},\frac{1}{4}, \cdots\right\}
=\left\{2^n\vert n \in \Bbb{Z}\right\}$
sorta!

$Q$ and $Q^\ast$ as above.
Find the order of each element in $Q$ and $Q^\ast$

ok is this like $4=2^2$

Nope.
The order of an element is the number of times we have to add (respectively multiply) it before we get the identity element.
So in $\mathbb Q$, how many times do we have to add $\frac 12$ before we get $0$?
And how many times do we have to add $0$ before we get $0$?
 

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