Page 3 - Lesson Notes

The angle in the pictures above is 37°.
( Do you see that there are two ways to measure an angle )

 perpendicular lines:
Perpendicular lines meet each other at an angle of 90°.

We say: line AB is perpendicular to line DC.

 perpendicular bisector

 line CD divides line segment AB into two equal parts then line CD is called the
perpendicular bisector of line segment AB.
 Let AB be a line segment. Mark its midpoint as M. Let MN be a line perpendicular to AB