# 7.9: Parallel Lines and Transversals

**At Grade**Created by: CK-12

**Practice**Parallel Lines and Transversals

What if you were given the street map, below, of Washington DC and told to find the missing street lengths?

### Watch This

CK-12 Foundation: Chapter7ParallelLinesandTransversalsA

Brightstorm: Proportional Segments Between Parallel Lines

### Guidance

The **Triangle Proportionality Theorem** states that if a line parallel to one side of a triangle intersects the other two sides, then it divides those sides proportionally. We can extend this theorem to a situation outside of triangles where we have multiple parallel lines cut by transverals.

**Theorem:** If three or more parallel lines are cut by two transversals, then they divide the transversals proportionally.

#### Example A

Find

The three lines are marked parallel, so you can set up a proportion.

#### Example B

Find

To solve, set up a proportion.

#### Example C

Find the value of

To solve, set up a proportion and solve for

Watch this video for help with the Examples above.

CK-12 Foundation: Chapter7ParallelLinesandTransversalsB

#### Concept Problem Revisited

To find

From this,

To find

### Vocabulary

Pairs of numbers are ** proportional** if they are in the same ratio. Two lines are

**if they have the same slope and thus never intersect. A**

*parallel***is a line intersecting a system of lines.**

*transversal*### Guided Practice

Find

Look at the corresponding segments. Only the segment marked “2” is opposite a number, all the other segments are opposite variables. That means we will be using this ratio, 2:3 in all of our proportions.

There are several ratios you can use to solve this example. To solve for

### Practice

Find the value of each variable in the pictures below.

The street map shows part of New Orleans. Burgundy St., Dauphine St. and Royal St. are parallel to each other. If Spain St. is perpendicular to all three, find the indicated distances.

- What is the distance between points
A andB ? - What is the distance between points
C andD ? - What is the distance between points
A andD ?

Using the diagram, answer the questions.

- What is the value of
w ? - What is the value of
x ? - What is the value of
y ? - What is the length of
AB¯¯¯¯¯¯¯¯ ? - What is the length of
AC¯¯¯¯¯¯¯¯ ?

Using the diagram, fill in the blank.

- If
b is one-thirdd , thena is ____________________. - If
c is two timesa , thenb is ____________________. -
This is a map of lake front properties. Find a andb , the length of the edge of Lot 1 and Lot 2 that is adjacent to the lake.

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Coordinate Plane

The coordinate plane is a grid formed by a horizontal number line and a vertical number line that cross at the (0, 0) point, called the origin. The coordinate plane is also called a Cartesian Plane.Perpendicular

Perpendicular lines are lines that intersect at a angle. The product of the slopes of two perpendicular lines is -1.Proportion

A proportion is an equation that shows two equivalent ratios.Quadrilateral

A quadrilateral is a closed figure with four sides and four vertices.transversal

A transversal is a line that intersects two other lines.Triangle Proportionality Theorem

The Triangle Proportionality Theorem states that if a line is parallel to one side of a triangle and it intersects the other two sides, then it divides those sides proportionally.### Image Attributions

Here you'll learn how to use the Triangle Proportionality Theorem with multiple parallel lines.