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A protractor is a helpful tool when it comes to constructing angles. It's a circular or semi-circular instrument used to measure angles in degrees, ranging from 0 to 180 or sometimes 360 degrees. Knowing how to properly use a protractor is key to accurately drawing angles.
To use a protractor to construct a 120-degree angle, start by placing the midpoint of the protractor's straight edge, often marked with a small hole or cross, right at the corner or vertex of the angle you're creating. Make sure that the base line of the protractor (usually the zero line) is aligned straight with the line you’ve drawn on your paper. This ensures precise measurement.
Next, follow the inner or outer scale of the protractor, depending on how it's oriented, and look for the 120-degree marking. Once you've located it, place a little mark on your paper at that point. This technique helps in constructing perfect angles without relying on guesswork.

• Ensure the protractor is aligned with the starting line.
• Use the correct scale (inner or outer) on the protractor.
• Accurately mark the degree point for precision.

Measuring angles is an essential skill in geometry that helps us understand shape, space, and sometimes motion. Angles are measured in degrees, which denote how open an angle really is. A degree is a measure of turn and forms a circle that completes at 360 degrees.
To measure an angle, you'll need to set up a baseline (starting line) and then utilize a tool like a protractor for the best accuracy. The center point of the protractor should sit at the vertex of the angle, to give a precise reading of where the second line should extend.
An angle measure tells you how wide an angle is, which can help in determining the type of angle. For instance, a 120-degree angle is an obtuse angle, as it's more than 90 degrees but less than 180 degrees. Knowing how to measure angles allows you to classify and construct them effectively.

• Degrees are the unit of angle measurement.
• 360 degrees make up a complete circle.
• Protractor is the common tool for measuring angles.

In geometry, angles are categorized based on their degree measurement. Understanding the different types of angles helps in identifying and working with various geometrical shapes and designs.
Here are some fundamental types of angles you should know:

• Acute angles: These are angles less than 90 degrees. They are sharp and small, like the tip of a pencil.
• Right angles: Exactly 90 degrees. They are the corners of square or rectangular objects.
• Obtuse angles: More than 90 degrees but less than 180 degrees. A 120-degree angle, for instance, falls into this category.
• Straight angles: Exactly 180 degrees. They look like a straight line.
• Reflex angles: More than 180 degrees. These angles appear to bend backward.

Understanding these types allows you to better appreciate geometry and aids in more complex problem-solving tasks related to angles.