### An Introduction to Galois Theory

This article only skims the surface of Galois theory and should probably be accessible to a 17 or 18 year old school student with a strong interest in mathematics.

### What's a Group?

Explore the properties of some groups such as: The set of all real numbers excluding -1 together with the operation x*y = xy + x + y. Find the identity and the inverse of the element x.

### Groups of Sets

The binary operation * for combining sets is defined as the union of two sets minus their intersection. Prove the set of all subsets of a set S together with the binary operation * forms a group.

# Sheep in Wolf's Clothing

##### Stage: 5 Challenge Level:

In the following exhibits we give an advanced or alternative way of thinking about mathematics concepts which are likely to be known in a more familiar form.

Explore these structures and experiment by substituting particular values such as $0, \pm 1$. Can you work out what they represent?

Exhibit A
All pairs of integers such that:
$$(a, b) + (c, d) = (ad+bc, bd)\quad\quad (Na, Nb) \equiv (a, b) \mbox{ for all } N\neq 0$$
Can you find two pairs which add up to give $(0, N)$ or $(0, M)$ for various values of $N$, $M$?

Next explore the properties of these structures:

Exhibit B

A set of ordered pairs of real numbers which can be added and multiplied such that

$(x_1, y_1) + (x_2, y_2) = (x_1 + x_2, y_1 +y_2)$

$(x_1, y_1)\times (x_2, y_2) = (x_1x_2 -y_1y_2, x_1y_2+y_1x_2)$

Exhibit C

A set defined recursively such that

$+_k(1) = +_1(k)$

$+_k(+_1(n)) = +_1(+_k(n))$

$\times_k(1) = k$

$\times_k(+_1(n)) = +_k(\times_k(n))$

In these rules, $k$ and $n$ are allowed to be any natural numbers

Once you have figured out what these structures represent ask yourself this: Are these good representations? What benefits can you see to such a representation? How might familiar properties from the structures be represented in these ways?