When 2 lines at a point and form a right angle are said to be perpendicular lines. The above diagram shows perpendicular lines.
When a line or angle is divided inequal parts by the use of compassess and straight edge, the line which divides the line or angle is known as the perpendicular bisector of that line or angle.The above picture shows the perpendicular bisector of a line.
When 2 lines go in a straight line such that they do not meet at any point ( As shown in the above diagram ) are said to be parallel lines.
