Finding the distance between two points given their coordinates
Math Open Reference

How to divide a line segment into N equal parts with compass and straightedge
Math Open Reference

How to copy a line segment with compass and straightedge
Math Open Reference

Definition of a congruent line segments
Math Open Reference

The definition of congruent. Congruent lines, angles shapes.
Math Open Reference

Points of concurrency  the point where three or more lines intersect
Math Open Reference

Definition and properties of concentric circles
Math Open Reference

Definition of 'Perpendicular Bisector'
Math Open Reference

Definition of 'Line Bisector' and a general discussion of bisection. Link to 'angle bisector'
Math Open Reference

Definition of 'base' and the various different ways the word is used in geometry
Math Open Reference
