# Lines and Angles (Module 4)

## G-CO.3.9

*Vertical angles are congruent;*

*when a transversal crosses parallel lines, alternate interior angles are congruent and corresponding angles are congruent; points on a perpendicular bisector of a line segment are [exactly those] equidistant from the segment’s endpoints.*## REMEMBER:

**Complementary angles**are angles whose measures have a sum of 90 degrees.

**Supplementary angles**are angles whose measures have a sum of 180 degrees.

## DEFINITION

In this diagram, which ray is the common side for the adjacent angles and ?

## In the diagram below, click and drag points A and C to change the measures of the angles.

What do you notice is always true about the linear pair of angles?

## DEFINITION

## In the diagram below, click and drag points A and C to change the measures of the angles.

What do you notice is always true about the vertical angles?

In the diagram above, which angles are vertical angles?

## Note the kinds of angles formed by 2 lines p and q, and transversal t. This diagram is also in your text (p. 175).

## Same-Side Interior Angles Postulate

If two parallel lines are cut by a transversal, then the same-side interior angles (like Angle Two and Angle Three) are

## Corresponding Angles Theorem

If two parallel lines are cut by a transversal, then the corresponding angles (like Angle One and Angle Four) are

## Alternate Interior Angles Theorem

If two parallel lines are cut by a transversal, then the alternate interior angles (like Angle One and Angle 3) are

## What is line CD?

In the diagram below, which of the following provides the **best** description of line CD as it relates to segment AB?

## Perpendicular Lines

## Click and drag point D.

While the lengths are changing, is there anything that is always true?