Measuring an Angle by a Protractor

In measuring an angle by a protractor, first we need to know what a protractor is.

Protractor:

It is an instrument for measuring or constructing an angle of a given measure. It is a circular or semicircular piece of metal or plastic.

It is a circular protractor which is marked in degrees from 0° to 360° from left as shown in adjoining figure.

It is a semicircular protractor which is marked in degrees from 0° to 180° from left as shown in adjoining figure.

For Example:

1. Use your protractor to draw 60°.

The centre O of the piece is also the midpoint of its base line. In order to measure ∠AOB, place the protractor in such a way that its centre is exactly on the vertex O of the angle, the base line lies along the arm OA. 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 we find ∠ AOB = 60°.



2. Use your protractor to draw 90°.

The centre O of the piece is also the midpoint of its base line. In order to measure ∠AOB, place the protractor in such a way that its centre is exactly on the vertex O of the angle, the base line lies along the arm OA. 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 we find ∠ AOB = 90°.

Related Links :



● Angle.

Interior and Exterior of an Angle.

Measuring an Angle by a Protractor.

Types of Angles.

Pairs of Angles.

Bisecting an angle.

Construction of Angles by using Compass.

Worksheet on Angles.

Geometry Practice Test on angles.

5th Grade Geometry Page

5th Grade Math Problems

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