question about proof

[May Day]

Let G be the group of symmetries of the square. Prove that g to the power 4 = 1, for every g belong to G.


could anyone give the process to show why it is equal to 1

 

[daon]

The first thing you should think about is what is the element 1 in G?

G is made up of rotations by an equivilance class of certain angles (what are they?) and vertical and horizontal flips.