Secant_tangent

f(x) = x
g(x) = cos(x)
h(x) = sin(x)
a = CurveCartesian(f(t), g(t), h(t), t, -15, 15)
v = 1.1 (slider from -5 to 5)
P: a(v)
r = Vector(P)
s = 1.1 (slider from 0 to 1.1, step 0.05)
Q: a(v + s)
w = Vector(Q)
b: (1 / s * Vector[P, Q])
c: w - r
d = Vector(a(v), a(v) + (b * v))
e = Vector(a(v), a(v) + (1.55 * UnitVector[a'(v)]))