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°.
● Angle.
Interior and Exterior of an Angle.
Measuring an Angle by a Protractor.
Construction of Angles by using Compass.
Geometry Practice Test on angles.
5th Grade Geometry Page
5th Grade Math Problems
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