Let G be the set of matrices $\displaystyle GL_2(R)$ over R.

Show that G is isomorphic to $\displaystyle Z_2 x Z_2$.

I know GL2R represents the matrices

1 0

0 1

-1 0

0 1

1 0

0 -1

-1 0

0 -1

But how can I show it is isomorphic to $\displaystyle Z_2 x Z_2$?