Calculation of an angle

From: FyD <fyd^at^u-picardie.fr>
Subject: Calculation of an angle
Date: Wed, 21 Apr 2004 20:52:12 +0200 (CEST)

Dear All,
 I am looking for an equation to calculate an angle from the cartesian
 coordinates of the 3 atoms making this angle.
 Thanks, Francois