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# Parallel and Perpendicular Lines - PowerPoint PPT Presentation

Parallel and Perpendicular Lines. Lines & Angles Section 3-1. Lines & Angles. Parallel Lines ( ll ) - are coplanar and do not intersect. Perpendicular Lines (⏊) – intersect at 90 ํ angles . Skew Lines – are not coplanar. Skew lines are not parallel and do not intersect.

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### Parallel and Perpendicular Lines

Lines & Angles

Section 3-1

• Parallel Lines (ll) - are coplanar and do not intersect.

• Perpendicular Lines (⏊) – intersect at 90ํangles.

• Skew Lines – are not coplanar. Skew lines are not parallel and do not intersect.

• Parallel Planes – are planes that do not intersect.

• **See diagram on pg. 146 for examples**

What are some examples of perpendicular lines??

• Transversal – a line that intersects two coplanar lines at two different points. The transversal t and the other two lines r and s for eight angles.

• Corresponding angles – lie on the same side of the transversal t, on the same sides of lines r and s. (∠1 & ∠5)

• Alternate interior angles – nonadjacent angles that lie on opposite sides of the transversal t, between lines r and s. (∠3 & ∠5)

• Alternate exterior angles – lie on opposite sides of the transversal t, outside lines r and s.(∠2 & ∠8)

• Same-side interior angles – lie on the same side of the transversal t, between lines r and s. (∠3 & ∠6)

### Angles formed by parallel lines & transversals

Section 3-2

• If two parallel lines are cut by a transversal, then the pairs of corresponding angles are congruent.

• Name the pairs of corresponding angles.

• If two parallel lines are cut by a transversal, then the pairs of alternate interior angles are congruent.

• What are the alt. int. angles?

• If two parallel lines are cut by a transversal, then the two pairs of alternate exterior angles are congruent.

• Exterior angles (using correct lingo on how to name an angle)??

• If two parallel lines are cut by a transversal, then the two pairs of same-side interior angles are supplementary.

• Example???

Name ‘em:

• Alternate Interior Angles:

• Alternate Exterior Angles:

Name ‘em:

• Corresponding Angles:

• Same-side: