\f. N(s) = di (s) K (S) : the unit normal vector (recall that k(s) = Ild5 (s)II.) . B(s) = T(s) x N(s) : the binormal vector.5. Show that a plane curve s > r(s) = (x(s), y(s)) with s e [0, 1] has zero torsion, that is T(s) = 0 for all s. Comment: You can think of a 2D curve in 3D by setting the last coordinate equal to 0; s - (r(s), y(s), 0). 6. Show that a plane curve s wr(s) = (x(s), y(s)) for s E 0, 1] with constant positive curvature k(s) = r > 0 for all s must be (a part of ) a circle