Concepts

An angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle
The sides of an angle are two rays that share a common endpoint called the vertex of the angle.
The vertex of an angle is the point where the two sides of an angle meet.

A protractor is used to measure and draw angles. There are two sets of degrees along the edge of the protractor: an inner and outer scale. Both scales go from 0 to 180 degrees, but they run in opposite directions. Each mark on the protractor is 1degree.
The baseline, also known as the zero edge, has a small circle at its midpoint. This is the center mark or origin point. 

Rules

How to draw an angle using a protractor:
1. Draw a ray (one side of the angle)
2. Place the center mark on the endpoint of the ray.
3. Starting from zero degrees, find the desired degree of the angle and make a mark.
4. Draw a ray from the vertex to the drawn mark.
5. The drawn angle will be the desired angle.

Example

Use the slider to estimate and draw an angle of 100°.

Estimation is acceptable within + 15°.

Solution

1. On the transparent protractor, the given side is lined up with zero on the outer scale. 

2. Note that a 90° angle (right angle) looks like the corner of a square. With this in mind, estimate where the second line would need to be drawn to get a 100° angle. 

3. Use the slider to draw the other side so it will be close to 100° on the outer scale. 

4. After drawing the line, click on the “check” box to see if the drawn line is within the acceptable limitations before submitting the answer.

Pre-requisite Skills

Estimation

Measuring Angles (4.10.1)