Measering Angles with protractors

One way an angle can be measured is by using a mathematical tool called a protractor. Below are two examples of a protractor.

source: (Chichos Caltech: http://www.chicos.caltech.edu/classroom/pointer/diagrams.htm)

source: (Clipart ETC: http://etc.usf.edu/clipart/25700/25799/protractor_25799.htm)

The protractor shown below has two scales:
The outer scale starts from 0° to180° going clockwise.

The inner scale starts from 0° to 180° going anti-clockwise.

source: (Clipart ETC: http://etc.usf.edu/clipart/25700/25799/protractor_25799.htm)

To measure an angle, follow these steps:

1. - place the origin or center (the part that is marked with the letter O on the left protractor, the small hole on the right protractor) part of the protractor on the vertex of the angle.
2. - Make sure that the base line on the protractor is lined with the arm of the angle.
3. - Check which numbers the other arm crosses over in the protractor. There are 2 sets of numbers that run along the protractor. Sometimes the arms of the angles are not long enough for the protractor, if that is the case then extend the arms with a ruler.
4. - Now, look at the angle you are measuring and ask yourself: "self is the angle an acute angle or an obtuse angle?"
5. - If the angle is acute or less than 90°, take the smaller number. If the angle is obtuse or greater than 90°, take the bigger number.

Look at the following example:

source: (Clipart ETC: http://etc.usf.edu/clipart/25700/25799/protractor_25799.htm)

To measure angle ABC , we need to:

Step 1: Place the center or origin of the protractor on the vertex B.

Step 2 : Adjust the base line so that it is aligned with the line BC.

Step 3: Look at the numbers the angle crosses on the protractor. The
numbers are 60 and 120.

Step 4: Ask yourself: "self, is this an obtuse or an acute angle?"

Step 5: It is an acute angle, so you would take the number in the inner
scale 60°.

Now, it is your turn, try it yourself!

Measure the following angles. Highlight the section below and print the selection.

Source: (Centre for Innovation in Mathematics Teaching: http://www.cimt.plymouth.ac.uk/projects/mepres/book8/bk8i11/bk8_11i1.htm)

source: (CSL Cartoonstock: http://www.cartoonstock.com/directory/A/Angles.asp)