Show that the curvature of a plane curve is k = |d/ds|, where is the angle

Show that the curvature of a plane curve is k = |dΦ/ds|, where Φ is the angle between T and i; that is, Φ is the angle of inclination of the tangent line. (This shows that the definition of curvature is consistent with the definition for plane curves given in Exercise 10.2.69.)