TangentToEllipse Definition

# Equation of the Tangent 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/t) .

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

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

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

end: