a = CurveCartesian(cos(t), sin(t), t, 0, (2 * π))
t0 = 2.14 (slider from 0 to (2 * π), step 0.01)
P: (cos(t0), sin(t0))
eq1: (cos(t0) * (x - cos(t0))) = ((-sin(t0)) * (y - sin(t0)))
mx: (-cot(t0))
my: (-tan(t0))