* The following material will provide assistance on the following exam problems – Essential Math II Exam 1 problem 20 Essential Math II Alternate Exam 1 problem 20

Using a Protractor to Measure and Construct Angles

Measuring Angles A protractor is tool used to measure angles. When measuring angles, follow these steps:

1. Place the vertex of the angle at the center of the crosshairs in the base of the protractor

2. Align the bottom line of your angle up with the horizontal portion of the crosshairs

3. If the bottom line points right, use the bottom set of numbers to measure your angle. If the bottom line points left, use the top set of numbers to measure your angle. It may be necessary to lengthen one or both of the lines of the angle. This will make determining the measure of the angle easier. The number that the upper line of your angle points to is the measure of the angle in degrees.

An example of how to measure an angle is given below. Notice that the lengths of the lines were made longer to make it easier to determine the measure of the angle.

The measure of the angle is 136°. E155-2

* Revised 10/17/03

Constructing Angles A protractor can also be used to construct, or draw angles. When constructing angles, follow these steps:

1. Place the protractor face up on the paper at the position you wish to construct the angle

2. With a pencil, place a dot at the center of the crosshairs in the base of the protractor.

3. Place a dot at either the left or right side of the base of the protractor at the horizontal marker corresponding to 0°.

4. Place a dot at the degree mark along the top of the protractor for the angle you wish to draw. If the 0° mark you chose was on the left, use the top set of numbers. If the 0° mark you chose was on the right, use the bottom set of numbers.

5. Remove the protractor and connect the two outer dots to the center dot. Be sure to use a straight edge like a ruler or the base of your protractor. DO NOT CONNECT THE TWO OUTTER DOTS TOGETHER

The following example will help you better understand how to use a protractor. An angle measuring 74° will be constructed. Step1: Place the Protractor face up on the paper.

E155-2

* Revised 10/17/03

Step2: Place a dot at the center of the crosshairs

Step3: Place a dot at either the left or right side of the base of the protractor at the horizontal marker corresponding to 0°.

E155-3

* Revised 10/17/03

Step4: Place a dot at the degree mark along the top of the protractor for the angle you wish to draw.

Step5: Remove the protractor and connect the two outer dots to the center dot.

E155-4

* Revised 10/17/03