How to have matrices side by side in latex?

Don't enclose each array with \[ ... \]; instead, put all the arrays that you want together within one set of delimeters. Like this:

\[ \left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right)
%
\left( \begin{array}{cc}
1 & 0 \\
0 & 1
\end{array} \right)
\]

You should read the mathmode documentation. It should be part of your TeX Distribution, and has lots of examples to follow.

This is slightly tangential, but you might find it convenient to use the pmatrix environment (defined in amsmath.sty)

\[
\begin{pmatrix}
  1 & 0 \\ 0 & e^{i\pi/k}
\end{pmatrix}
\begin{pmatrix}
  u \\ v
\end{pmatrix}
=
\begin{pmatrix}
  u \\ -v
\end{pmatrix}
\]

The idea is to enclose both matrices in one block i.e. \[ \] see this example

\[
\begin{bmatrix}
    a  &  b      \\
    c  &  d      
\end{bmatrix}
= 
\begin{bmatrix}
    8  &  1      \\
    7  &  6      
\end{bmatrix} 
\]

It will be something like:

enter image description here

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