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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