NormalToEllipse Definition

# Equation of the Normal to the parametric ellipse,
# at a parametric point, centered at the point c
# and having axes of lengths d[1],d[2], with parameter t
# It uses the fact that the slope, dy/dx equals (dy/dt)/(dx/dt).

NormalToEllipse:=proc(c,d,t) local P:

P:=ParEllipse (c,d,t):

diff(P[2],t)*(y-P[2])+diff(P[1],t)*(x-P[1]):

end: