A parametric curve r(t) crosses itself if there exist t + s such that r(t) = r(s). The angle of intersection is the (acute) angle between the tangent vectors r'(t) and r'(s). The parametric curve r = (t² - 4t+ 2, −3 cos(πt), t³ – 16t) crosses itself at one and only one point. The point is (x, y, z) = = ( Let be the acute angle between the two tangent lines to the curve at the crossing point. Then cos(e)