Let P be an interior point of an acute-angled triangle ABC. The line BP meets the line AC at E, and the line CP meets the line AB at F. The lines AP and EF intersect each other at D. Let K be the foot of the perpendicular from the point D to the line BC. Show that the line KD bisects the angle ∠EKF. trigonometrygeometryalgebrapolynomialangle bisector