### Lesson 1.5: Angle Measurement

We measure a line segment’s
*
length
*
with a ruler. Angles are measured with something called a
**
protractor
**
. A protractor is a measuring device that measures how “open” an angle is. Angles are measured in degrees, and labeled with a
symbol.

The
**
Angle Addition Postulate
**
states that if
is on the interior of
, then
. See the picture below.

### Ticket In/Ticket Out Activity:

#### Example A

Measure the three angles using a protractor.

#### Example B

What is the measure of the angle shown below?

#### Example C

What is in the diagram below?

#### Example D

Draw a angle.

### Vocabulary

A
**
protractor
**
is a measuring device that measures how “open” an angle is. Angles are measured in

**, and labeled with a symbol. A**

*degrees***is a tool used to draw circles and arcs.**

*compass*### Warm-Up Activity/Guided Practice:

1. Use a protractor to measure below.

2. What is if and ?

3. If , find and and ?

### Practice

1. What is if and ?

2. If , find .

For questions 3-6, determine if the statement is true or false.

- For an angle is the vertex.
- For an angle and are the sides.
- The in front of means measure.
- The Angle Addition Postulate says that an angle is equal to the sum of the smaller angles around it.

For 7-12, draw the angle with the given degree, using a protractor and a ruler.

For 13-16, use a protractor to determine the measure of each angle.

Solve for .