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# Parallel and Perpendicular Lines

## Parallel, perpendicular, and intersecting lines

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Practice Parallel and Perpendicular Lines
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Identify Types of Lines

Have you ever had a math question that you couldn't figure out? Take a look at this dilemma.

Candice saw the following illustration in her math book.

She wondered how to describe the relationship between the brown plane and the green plane.

Do you know how to identify this relationship? This Concept will teach you how to help Candace with her dilemma.

### Guidance

In other math classes, you learned about different types of lines. Lines exist in space. Two lines intersect when they cross each other. Because all lines are straight, intersecting lines can only cross each other once.

There are parallel lines, intersecting lines and perpendicular lines. Let’s start by briefly reviewing these terms and then we can look at the angles formed when these lines intersect.

Types of Lines

Parallel Lines are lines that are an equal distance apart. This means that these lines will never intersect.

Intersecting lines are lines that cross at some point.

Perpendicular lines are lines that intersect at a angle.

#### Example A

Lines that will never cross are called?

Solution: Parallel lines

#### Example B

Lines that meet at a are called?

Solution: Perpendicular

#### Example C

An intersection is an example of what type of lines?

Solution: Intersecting lines

Now let's go back to the dilemma from the beginning of the Concept.

If you look at these two planes, you will see that they are equidistant. This means that they are the same distance apart and will never intersect. Because these two planes will never intersect, we can say that they are parallel.

### Vocabulary

Parallel lines
lines that are an equal distance apart and will never intersect.
Intersecting lines
lines that cross at one point.
Perpendicular lines
lines that intersect at a angle and form two or more angles.
Angle
the measure of the space formed by two intersecting lines.
Straight angle
is a straight line equal to .

### Guided Practice

Here is one for you to try on your own.

What is the relationship between STC and ATC?

Solution

These two angles meet at a right angle, and so the value of each angle is . Therefore, the angles are perpendicular angles.

### Practice

Directions: Name each type of lines shown below.

1.

2.

3.

4.

Directions: Write the definitions for the following types of lines.

1. Parallel lines
2. Intersecting lines
3. Perpendicular lines

1. What is the symbol for parallel lines?
2. What is the symbol for perpendicular lines?
3. An intersection on a highway is an example of what type of lines?
4. A four way stop is an example of what type of lines?
5. Is it possible for intersecting lines to also be considered perpendicular?

Directions: Describe the types of lines shown in each illustration.

13.

14.

15.

### Vocabulary Language: English

Angle

Angle

A geometric figure formed by two rays that connect at a single point or vertex.
Intersecting lines

Intersecting lines

Intersecting lines are lines that cross or meet at some point.
Parallel

Parallel

Two or more lines are parallel when they lie in the same plane and never intersect. These lines will always have the same slope.
Perpendicular lines

Perpendicular lines

Perpendicular lines are lines that intersect at a $90^{\circ}$ angle.
Straight angle

Straight angle

A straight angle is a straight line equal to $180^{\circ}$.