Chapter 11.5, Problem 46AYU

Show that if n and j are integers with $0\le j\le n$, then

$\left(\begin{array}{l}n\\ j\end{array}\right)=\left(\begin{array}{l}n\\ n-j\end{array}\right)$

Conclude that the Pascal triangle is symmetric with respect to a vertical line drawn from the topmost entry.