Protractor in Math - Definition, How to Use a Protractor, FAQs - Free Printable

The image shows a protractor with two angles being measured: ∠AOC and ∠BOC. Let's understand how to read the protractor and interpret the given angles.

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🔍 Understanding the Protractor

A protractor is a tool used to measure angles in degrees (°). It is typically semi-circular and marked from 0° to 180°, with two scales:
- The outer scale (clockwise from 0° on the left)
- The inner scale (counterclockwise from 0° on the right)

In this diagram:
- Point O is the center of the protractor.
- Line AB is a straight line passing through O, forming a straight angle of 180°.
- Ray OC is drawn from point O, creating two angles:
- ∠AOC (from A to C)
- ∠BOC (from B to C)

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✔ Step-by-step Reading of the Angles

#### 1. ∠AOC = 60°
- Start at point A (left end of the baseline).
- Follow the inner scale (since the angle opens upward from the left side).
- The ray OC points to 60° on the inner scale.
- So, ∠AOC = 60°

#### 2. ∠BOC = 120°
- Start at point B (right end of the baseline).
- Follow the outer scale (since the angle opens upward from the right side).
- The ray OC points to 120° on the outer scale.
- So, ∠BOC = 120°

> ⚠️ Note: The total angle around point O along the straight line AB is 180°.
> So, ∠AOC + ∠BOC = 60° + 120° = 180°, which confirms they form a straight line.

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📌 Key Tips for Reading a Protractor

1. Place the protractor correctly: Align the center of the protractor (the small hole or mark) with the vertex of the angle (point O).
2. Align one arm of the angle with the baseline of the protractor (here, AB).
3. Read the scale that starts from 0° at the aligned arm.
4. Follow the other arm to see where it intersects the scale — that’s your angle measurement.

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✔ Final Answer:

- ∠AOC = 60°
- ∠BOC = 120°

These measurements are correct based on proper use of the protractor.

Let me know if you'd like a step-by-step guide on measuring an angle with a protractor!