The lateral sidelines AB and CD of trapezoid ABCD meet at point S. The bisector of angle ASC meets the bases of the trapezoid at points K and L (K lies inside segment SL). Point X is chosen on segment SK, and point Y is selected on the extension of SL beyond L such a way that ∠AXC−∠AYC=∠ASC. Prove that ∠BXD−∠BYD=∠BSD. geometrytrapezoidanglesequa angles