The degree is the standard unit for measuring angles.
The mathematical symbol of degree is °.
An instrument Protractor is used to measure angles in degrees. You can find protractor in your geometry box.
Protractors have two scales:
- Inner scale
- Outer scale
The two scales have numbers starting from 0 till 180.
A protractor can be used to read and measure angles from left to right and from right to left as well. The baseline of the protractor joins 0° to the centre.
How to measure angles using a protractor?
Consider ∟XYZ.
Step 1: Place the centre of the protractor at the vertex Y. Arm YZ should be on the baseline of the protractor.
Step 2: Read the marking on the inner scale of the protractor at the point where arm YX intersects the scale. Here reading of the protractor is 40°.
Measure of ∟XYZ = 40° or m ∟XYZ = 40°.
Remember: Read markings on the outer circle when the baseline of an angle points towards the left zero of the protractor.
Here, ∟AOB = 45°
The rule: Use the inner scale when the baseline point towards the right zero and use the outer scale when the baseline point towards left zero.
Remember: Right in left out or RILO.
Exercise 8.1
