Parallel and Perpendicular Lines

Lines & AnglesSection 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.

• Parallel Planes – are planes that do not intersect.

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

What are some examples of perpendicular lines??

Examples:

Angle Pairs formed by a Transversal• 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

Corresponding Angles Postulate• If two parallel lines are cut by a transversal, then the pairs of corresponding

angles are congruent.

• Name the pairs of corresponding angles.

Alternate Interior Angles Theorem• If two parallel lines are cut by a transversal, then the pairs of alternate interior

angles are congruent.

• What are the alt. int. angles?

Alternate Exterior Angles Theorem• 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)??

Same-Side Interior Angles Theorem• 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:

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• Alternate Exterior Angles:

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Name ‘em:• Corresponding Angles:

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• Same-side:

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