a = 3 (slider from 1 to 8, step 1)
b = 1 (slider from 1 to 8, step 1)
t = 2.6179939500000002 (slider from 0 to 6.283185307179586, step 0.17453293)
f(x) = a * cos(x)
g(x) = b * sin(x)
c: x^(2) / a^(2) + y^(2) / b^(2) = 1
f_x = Derivative(f, x)
g_x = Derivative(g, x)
f_{xx} = Derivative(f_x, x)
g_{xx} = Derivative(g_x, x)
P: (f(t), g(t))
l(x) = f(x) - ((f_x(x)^(2) + g_x(x)^(2)) * g_x(x)) / (f_x(x) * g_{xx}(x) - f_{xx}(x) * g_x(x))
m(x) = g(x) + ((f_x(x)^(2) + g_x(x)^(2)) * f_x(x)) / (f_x(x) * g_{xx}(x) - f_{xx}(x) * g_x(x))
Q: (l(t), m(t))
d = Circle(Q, P)
k_1(x) = (f_x(x) * g_{xx}(x) - f_{xx}(x) * g_x(x)) / (f_x(x)^(2) + g_x(x)^(2))^(3 / 2)
κ: k_1(t)
κ_{r}: 1 / Distance[P, Q]