Geometry: Chapter 3

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# Geometry: Chapter 3 - PowerPoint PPT Presentation

Geometry: Chapter 3. Ch. 3. 4: Prove Lines are Parallel Ch. 3.5 Using Properties of Parallel Lines. Postulate 16: Corresponding Angles Converse If two lines are cut by a transversal so the corresponding angles are congruent, then the lines are parallel.

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### Geometry: Chapter 3

Ch. 3. 4: Prove Lines are Parallel

Ch. 3.5 Using Properties of Parallel Lines

Postulate 16: Corresponding Angles Converse

If two lines are cut

by a transversal so

the corresponding

angles are congruent,

then the lines are parallel.

Image taken from: Geometry. McDougal Littell: Boston, 2007. P. 161.

Ex. 1. Find the value of y that makes a || b.

Image taken from: Geometry. McDougal Littell: Boston, 2007. P. 162.

Ex. 1 (cont.)

Solution: Lines a and b are parallel if the marked alternate exterior angles are congruent.

(5y +6)o =121o

5y=121-6

5y=115

y = 23

Theorem 3.8: Alternate Interior Angles Converse

If two lines are cut

by a transversal so the

alternate interior angles

are congruent, then the

lines are parallel.

Image taken from: Geometry. McDougal Littell: Boston, 2007. P. 162.

Theorem 3.9: Consecutive Interior Angles Converse

If two lines are cut

by a transversal so the

consecutive interior

angles are supplementary,

then the lines are parallel.

Image taken from: Geometry. McDougal Littell: Boston, 2007. P. 162.

Theorem 3.10: Alternate Exterior Angles Converse

If two lines are cut

by a transversal so the

alternate exterior angles

are congruent, then the

lines are parallel.

Image taken from: Geometry. McDougal Littell: Boston, 2007. P. 162.

Example 2: A woman was stenciling this design on her kitchen walls. How can she tell if the top and bottom are parallel?

She can measure alternate interior angles or corresponding angles and see if they are congruent.

Image taken from: Geometry. McDougal Littell: Boston, 2007. P. 162.

Image taken from: Geometry. McDougal Littell: Boston, 2007. P. 163.

Theorem 3.11: Transitive Property of Parallel Lines.

If two lines are parallel to the same line, then they are parallel to each other.

Theorem 3.12: Lines Perpendicular to a Transversal Theorem

In a plane, if two lines are perpendicular to the same line, then they are parallel to one another.

If m┴ p and n┴ p,thenm || n.

Image taken from: Geometry. McDougal Littell: Boston, 2007. P. 192.