Perpendicular Bisector

A perpendicular bisector is a particular type of line that intersects another line at a 90º angle, and the line it crosses is divided into two equal portions. Take for example the following lines:

Perp bisect - 1.png

In the above figure, AD is the perpendicular bisector to BC. That means that both ∠ADC and ∠ADB = 90º and that the length of BD and DC are the same length. So, D is the midpoint to BC.