2. You will learn to describe relationships among lines, parts of lines, and planes. In geometry, two lines in a plane that are always the same distance apart are ____________. parallel lines No two parallel lines intersect, no matter how far you extend them.

3. Definition of Parallel Lines Two lines are parallel if they are in the same plane and do not ________. -This means the lines never touch -This means the lines have the same slope -This means the lines are always the same distance apart -The symbol for parallel is two vertical lines (II). For example if line m and line t are parallel you could write m II t. intersect

4. You will learn to identify the relationships among pairs of interior and exterior angles formed by two parallel lines and a transversal.

5. In geometry, a line, line segment, or ray that intersects two or more lines at different points is called a __________ transversal l m B A is an example of a transversal. It intercepts lines l and m. Note all of the different angles formed at the points of intersection. 1 2 34 5 7 6 8

6. Definition of Transversal In a plane, a line is a transversal if it intersects two or more lines, each at a different point. The lines cut by a transversal may or may not be parallel. l m 1 2 3 4 5 7 6 8 Parallel Lines t is a transversal for l and m. t 1 2 3 4 5 7 6 8 b c Nonparallel Lines r is a transversal for b and c. r

7. Two lines divide the plane into three regions. The region between the lines is referred to as the interior. The two regions not between the lines is referred to as the exterior. Exterior Interior

8. l m 1 2 3 4 5 7 6 8 When a transversal intersects two lines, _____ angles are formed. eight These angles are given special names. t Interior angles lie between the two lines. Exterior angles lie outside the two lines. Alternate Interior angles are between the two lines on the opposite sides of the transversal. Consectutive Interior angles or same side interior angles between the two lines are on the same side of the transversal. Alternate Exterior angles are outside the two lines on the opposite sides of the transversal.

9. Alternate Interior Angles If two parallel lines are cut by a transversal, then each pair of Alternate interior angles is _________. (equal) Angles 4 and 6 are alternate interior angles so we know 1 2 3 4 5 7 6 8 congruent

10. 1 2 3 4 5 7 6 8 Consecutive Interior Angles If two parallel lines are cut by a transversal, then each pair of consecutive interior angles is _____________. (add to 180) Angles 4 and 5 are consecutive interior angles so we know: supplementary

11. 1 2 3 4 5 7 6 8 Alternate Exterior Angles If two parallel lines are cut by a transversal, then each pair of alternate exterior angles is _________. Angle 1 and 7 are alternate exterior angles so we know: congruent

12. You will learn to identify the relationships among pairs of corresponding angles formed by two parallel lines and a transversal.

13. l m 1 2 3 4 5 7 6 8 t When a transversal crosses two lines, the intersection creates a number of angles that are related to each other. Note  1 and  5 below. Although one is an exterior angle and the other is an interior angle, both lie on the same side of the transversal. Angle 1 and 5 are called __________________. So <1=<5 corresponding angles

14. Corresponding Angles If two parallel lines are cut by a transversal, then each pair of corresponding angles is _________. congruent

15. Concept Summary CongruentSupplementary alternate interior alternate exterior corresponding consecutive interior or same side interior same side exterior Types of angle pairs formed when a transversal cuts two parallel lines.