Let ABC be a triangle with ∠BAC=40∘ and ∠ABC=60∘. Let D and E be the points lying on the sides AC and AB, respectively, such that ∠CBD=40∘ and ∠BCE=70∘. Let F be the point of intersection of the lines BD and CE. Show that the line AF is perpendicular to the line BC. trigonometrygeometrycircumcircletrig identitiesLaw of Sinesgeometry unsolved