What if you wanted to group different angles into different categories? After completing this Concept, you'll be able to classify angles geometrically.

### Watch This

CK-12 Foundation: Chapter1AngleClassificationA

James Sousa: Animation of Types of Angles

### Guidance

By looking at the protractor we measure angles from

**Straight Angle:** When an angle measures

**Right Angle:** When an angle measures

Notice the half-square, marking the angle. This marking is always used to mark right, or

**Acute Angles:** Angles that measure between

**Obtuse Angles:** Angles that measure between

It is important to note that

Any two lines or line segments can intersect to form four angles. If the two lines intersect to form right angles, we say the lines are **perpendicular**.

The symbol for perpendicular is

There are several other ways to label these two intersecting lines. This picture shows **two perpendicular lines, four right angles, four** **angles**, and even **two straight angles,**

#### Example A

Name the angle and determine what type of angle it is.

The vertex is **obtuse**.

#### Example B

What type of angle is

**obtuse**.

#### Example C

What type of angle is

**acute**.

Watch this video for help with the Examples above.

CK-12 Foundation: Chapter1AngleClassificationB

### Guided Practice

Name each type of angle:

1.

2.

3.

**Answers:**

1. Right

2. Acute

3. Straight

### Interactive Practice

### Explore More

For exercises 1-5, determine if the statement is true or false.

- Two angles always add up to be greater than
90∘ . 180∘ is an obtuse angle.180∘ is a straight angle.- Two perpendicular lines intersect to form four right angles.
- A right angle and an acute angle make an obtuse angle.

For exercises 6-11, state what type of angle it is.

55∘ 92∘ 178∘ 5∘ 120∘ 73∘ - Interpret the picture to the right. Write down all equal angles, segments and if any lines are perpendicular.
- Draw a picture with the following requirements.

In 14 and 15, plot and sketch

A(5,−3),B(−3,−1),C(2,2) A(−3,0),B(1,3),C(5,0)

### Answers for Explore More Problems

To view the Explore More answers, open this PDF file and look for section 1.6.