The second volume of the first day of junior high school mathematics-the middle vertical line of the line segment
PA, PB and PC are equal in length. First of all, point P is on the perpendicular of AB, so PA=PB, and similarly P is on the perpendicular of BC, and PB=PC, so PA=PB=PC. Because PA=PC, point p is also on the perpendicular line of AC. Proof of typical three-in-one