2. As shown in the figure, in the known triangle ABC, AD is the bisector of the angle BAC, DE is perpendicular to AB and E, and DF is perpendicular to AC and F, which proves that AD is the middle vertical line of EF.
3. In trapezoidal ABCD, AB//DC, E is the midpoint of waist AD, AB+DC=BC, which proves that BE is perpendicular to CE.