Angles & Angle Measurement | Student Worksheet

The Big Idea

An angle is formed when two rays share the same endpoint (called the vertex).

We measure angles in degrees. A full turn is 360 degrees!

Types of Angles

Acute

Less than 90°

Right

Exactly 90°

Obtuse

90° to 180°

Straight

Exactly 180°

How to Use a Protractor

1Find the center

Place the center point of the protractor on the vertex (corner) of the angle.

2Align the baseline

Line up one ray of the angle with the 0° line on the protractor.

3Read the scale

Find where the other ray crosses the scale and read the number.

4Check your work

Does your answer make sense? Acute should be less than 90°!

Pro Tip: The protractor has TWO scales! Always estimate first - if the angle looks acute, the answer should be less than 90°. If it looks obtuse, the answer should be more than 90°.

Angle Addition: When Angles Share a Side

If two angles share a side, you can ADD them!

35° + 55° = 90°

Together they make a right angle!

Finding unknown angles: If the total is 120° and one part is 45°, the other part is 120° - 45° = 75°

Your Turn: Practice Problems

1. Classify each angle as acute, right, obtuse, or straight:

a) 45° = b) 90° =

c) 135° = d) 180° =

2. Is this angle acute, right, or obtuse?

This angle is

3. Two angles share a side. One angle is 40° and the other is 50°. What is the total?

40° + 50° =

4. An angle measures 115°. What type of angle is it?

5. Two angles share a side. Together they make 90°. If one angle is 25°, what is the other?

90° - 25° =