Measuring an Angle

We will discuss here about measuring an angle with the help of a protractor.

You can find it in your Geometry Box. It has the semi-circular shape. Its semi-circular edge is divided into 180 divisions. Each division represents a degree denoted by °.

Measuring an Angle

There are two scales marked on the protractor – outer and inner. The outer scale is marked from 0° to 180° in clockwise direction.

To measure the given ∠MON, we place the protractor in such way that its centre is on the vertex O of ∠MON and its straight horizontal edge lies on the arm ON of the ∠MON as shown in figure.

Measuring Angles with a Protractor

Now we see which degree mark on the scale of the protractor, the arm OM coincides with. In the given figure, OM coincides with 90°. So, the ∠MON measures 90°.






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