|\angle BCA| + |\angle ABD| = |\angle BDA| + |\angle ACD| => KL//AC
Source: Czech And Slovak Mathematical Olympiad, Round III, Category A 2013 p5
February 15, 2020
anglesparallelogramparallelgeometry
Problem Statement
Given the parallelogram such that the feet of the perpendiculars from point on the sides respectively are internal points. Prove that when .