3. Show that if there is a unit vector a such that the tangent indicatrix T of a closed and regular curve a : [a, b] R2 satisfies T(t) + a, for all te [a,b], then, CT(a) = 0. Give an example where this situation occurs. Note that CT(a) denotes the total curvature of a. 4. Let 2 0. si s 0. si s