CK12 - Geometry

of the two measurements.Of course,startingwith one side at zero is usuallyeasier. Examples5 and 6
showhow to use a protractorto measureangles.

NotationNote: Whenwe talk aboutthe measureof an angle,we use the symbols. So for example,

if we useda protractorto measure in example3 and we foundthat it measured120º,we could

write.

Example 5

Whatis the measureof the angleshownbelow?

This angleis linedup with a protractorat 0º, so you can simplyread the final numberon the protractoritself.
Rememberyou can checkthat you are usingthe correctscaleby makingsure your answerfits your angle.
If the angleis acute,the measureof the angleshouldbe less than 90º. If it is obtuse,the measurewill be
greaterthan 90º. In this case,the angleis acute,so its measureis 50º.

Example 6

Whatis the measureof the angleshownbelow?

This angleis not linedup with the zero markon the protractor, so you will haveto use subtractionto find
its measure.

Usingthe innerscale,we get.

Usingthe outerscale,.

Noticethat it doesnot matterwhichscaleyou use. The measureof the angleis 125º.

Example 7

Use a protractorto measure below.