 
 
Finding the tangent vector is easy.  If we think of t as time, then the
vector   gives our position on C as a function of time.  Thus,
our velocity vector is always tangent to our path.  But, we know that
  gives our position on C as a function of time.  Thus,
our velocity vector is always tangent to our path.  But, we know that
  
 
so that means that at each of the N + 1 points, we have
  
 
This relationship is really just the differential form of the familiar 
equation ``distance = rate   time''.  Note that
  time''.  Note that   is
really a displacement vector between the ith and i+1th points on the 
curve C and
  is
really a displacement vector between the ith and i+1th points on the 
curve C and   is the time it takes to get from the ith to the
i+1th point.  In general, we take a uniform step between points so that
  is the time it takes to get from the ith to the
i+1th point.  In general, we take a uniform step between points so that
  .
 .