How can I draw this shape:

Question

I want to draw this matrix but I can't.

Answer 1

This might be a solution:

\documentclass{article}

\begin{document}
\[%
\begin{array}{ccccc}
  a_1 & a_2 & a_3 & \ldots & a_n\\
  1 & 0 & 0 & \ldots & 0 \\
  0 & 1 & 0 & \ldots & 0 \\
  0 & 0 & 1 & \ldots & 0 \\
  \vdots & \vdots & \vdots & \ddots & \vdots \\
  0 & 0 & 0 & \ldots & 1 
\end{array}%
\]
\end{document}

althoug I am not shure, if I got the last row and column right.

This is the result