# 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.**

**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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