Concave angles can be measured directly with a protractor. The protractor is placed exactly on the angle's vertex, and the degree value is read from where the other side of the angle intersects the protactor. The protractor has two scales, and it is important to choose the correct scale when measuring an angle. The choice of an erroneous scale is avoided by keeping in mind what acute and obtuse angles look like and what their degree values must be.

Example 1

Measure the degree of the angle [[$\beta$]] .

This angle is an example of a convex angle, the degree of which cannot be measured directly with a protractor. First, measure the proportion of the acute angle that is missing from the full angle. Subtracting this from 360 ° gives the angle asked.

Bisecting an angle with a protractor

An angle can be bisected with the help of a protractor.