1. Intersecting Lines – Coplanar lines that share one common point.
Review:
Intersecting Lines – Coplanar lines that share one common point. A B D E C
Symbol: Ç
Example:
AC Ç BE at D.

2. Example: BD ^ AC Lines that intersect to form right angles. Symbol: ^
Perpendicular Lines
Lines that intersect to form right angles. A B D C
Symbol: ^
Example:
BD ^ AC

3. Three or more lines that intersect at the same point.
Concurrent Lines
Three or more lines that intersect at the same point. A B D F G H K
Example:
AG, BF, and DH are concurrent lines and intersect at point K.

4. Example: AB // CD Definition – coplanar lines that do not intersect
Parallel Lines
Definition – coplanar lines that do not intersect
Symbol: // A B C D
Example:
AB // CD

5. Skew Lines
Example
Definition – noncoplanar lines. Therefore, they are neither parallel, nor intersecting.
EG and AB are skew lines

6. Definition – planes that do not intersect.
Parallel Planes
Definition – planes that do not intersect.
Examples:
GFDE and HCBA
GHAE and DBCF

7. Name each figure using proper notation.
Check for Understanding
1. Two parallel lines.
2. Two parallel planes.
3. Two skew lines.
4. Two intersecting planes.
5. Two intersecting lines.
6. Three concurrent lines.
7. Four coplanar points.
8. Two perpendicular lines.
Figure is a cube.
Name each figure using proper notation.

8. Figure is a cube. Check for Understanding 1. ED Ç DB 2. EDFG Ç DFCB
3. Classify GE and DF.
4. Classify GE and DB.
5. Classify GE and EA.
6. Classify GE and BC.
Point D DF
Parallel
Figure is a cube.
Skew
Intersecting or Perpendicular
Parallel

9. Transversal
Definition – a line that intersects two or more coplanar lines in different points.
Note: the “two or more coplanar lines” do NOT have to be parallel.

10. Pairs of Angles
When two lines cut by a transversal several pairs of angles are formed.

11. Pairs of Angles 2 1
Corresponding Angles

12. Pairs of Angles 3 1
Alternate Interior Angles

13. Pairs of Angles 5 4
Alternate Exterior Angles

14. Pairs of Angles 6 1
Same Side Interior Angles

15. Pairs of Angles 2 4
Same Side Exterior Angles

16. Pairs of Angles 5 2 3 6 7 1 8 4