Measuring an Angle by a Protractor

Measuring an Angle by a Protractor | How to Use a Protractor to Draw an Angle?

Protractor helps you to measure the angles in degrees. In this article, the students of 5th grade math can learn how to make a neat angle using the protractor. The symbol for degrees is a small circle °. A protractor has two sets of numbers from 0 to 180 and the other set from 180 to 0. In order to measure the angle with a protractor, the students must know what is a protractor. Read this page thoroughly to know how to find the angle with protractor with examples.

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What is a Protractor?

The size of an angle is measured using a protractor. The shape of a protractor is a semicircle. The semicircle is divided into two parts. The protractor has two sets of measurements. The first set is from 0° to 180° and the other set is from 180° to 0°. The marking on the inner circle is 0 degrees to 180 degrees in the opposite direction to the markings on the outer circle.

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How to Measure an Angle with a Protractor?

  • First place the midpoint of the protractor on the vertex of the angle.
  • Line up one side of the angle with zero lines of the protractor.
  • Read the degrees where the other side crosses the number line.

Example: What is the measure of 90° in a protractor?
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Measuring Angles with a Protractor Examples

Have a look at the below examples to see how to make a neat angle using a protractor.

Example 1.
Use your protractor to draw 75°.
Solution:
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1. The centre O of the piece is also the midpoint of its baseline.
2. To measure ∠AOB, place the protractor in such a way that its center is exactly on the vertex O of the angle, the baseline lies along the arm OA.
3. We need to read the mark through which the arm OB passes, starting from O on the side A, as we observe in the above figure.
Thus ∠AOB = 75°.

Example 2.
Use your protractor to draw 120°.
Solution:
Protractor_3
1. The center O of the piece is also the midpoint of its baseline.
2. To measure ∠AOB, place the protractor in such a way that its center is exactly on the vertex O of the angle, the baseline lies along the arm OA.
3. We need to read the mark through which the arm OB passes, starting from O on the side A, as we observe in the above figure.
Thus ∠AOB = 120°.

Example 3.
Use your protractor to draw 35°.
Solution:
Protractor_4
1. The center O of the piece is also the midpoint of its baseline.
2. To measure ∠AOB, place the protractor in such a way that its center is exactly on the vertex O of the angle, the baseline lies along the arm OA.
3. We need to read the mark through which the arm OB passes, starting from O on the side A, as we observe in the above figure.
Thus ∠AOB = 35°.

Example 4.
Use your protractor to draw 15°.
Solution:
Protractor_5
1. The center O of the piece is also the midpoint of its baseline.
2. To measure ∠AOB, place the protractor in such a way that its center is exactly on the vertex O of the angle, the baseline lies along the arm OA.
3. We need to read the mark through which the arm OB passes, starting from O on the side A, as we observe in the above figure.
Thus ∠AOB = 15°.

Example 5.
Use your protractor to draw 50°.
Solution:
Protractor_6
1. The center O of the piece is also the midpoint of its baseline.
2. To measure ∠AOB, place the protractor in such a way that its center is exactly on the vertex O of the angle, the baseline lies along the arm OA.
3. We need to read the mark through which the arm OB passes, starting from O on the side A, as we observe in the above figure.
Thus ∠AOB = 50°.

FAQs on Using a Protractor to Measure Angles

1. How do you use a protractor to measure degrees?

1. Place the midpoint of the protractor on the vertex of the angle.
2. Line up one side of the angle with the zero lines of the protractor.
3. Read the degrees where the other side crosses the number scale.

2. Do you use the inside or outside numbers on a protractor?

Both scales go from 0 to 180, but they run in opposite directions. If the angle opens to the right side of the protractor, use the inner scale. If the angle opens to the left of the protractor, use the outer scale.

3. What are the lines on a protractor called?

A straight line, which is displayed in the horizontal direction at the bottom of a protractor is called the baseline of the protractor.

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