You can eitherline it up with zero,or line it up with anothernumberand find the absolutevalueof the differ-
encesof the anglemeasuresat the endpoints.Eitherway, the resultis 100º.The anglemeasures100º.
AngleAdditionPostulate
You havealreadyencounteredthe rulerpostulateand the protractorpostulate.Thereis also a postulate
aboutanglesthat is similarto the SegmentAdditionPostulate.
AngleAdditionPostulate: The measureof any anglecan be foundby addingthe measuresof the smaller
anglesthat compriseit. In the diagrambelow, if you add and , you will havefound
.Use this postulatejust as you did the segmentadditionpostulateto identifythe way differentanglescombine.
Example 8
Whatisin the diagrambelow?
You can see that is 15º. You can also see that is 30º. Usingthe angleadditionpos-tulate,you can add thesevaluestogetherto find the total.