Beginby namingthis angle.It has threepointslabeledand the vertexis. So, the anglewill be named
or just. For the classification,comparethe angleto a right angle. openswiderthan
a right angle,and less than a straightangle.So, it isobtuse.
Example 4
Whatterm best describesthe angleformedby Clintonand Reevestreetson the map below?The intersectingstreetsform arightangle. It is a squarecorner, so it measures90º.ProtractorPostulate
In the last lesson,you studiedthe ruler postulate.In this lesson,we’ll exploretheProtractorPostulate.As
you can guess,it is similarto the ruler postulate,but appliedto anglesinsteadof line segments.A protractor
is a half-circlemeasuringdevicewith anglemeasuresmarkedfor eachdegree.You measureangleswith
a protractorby liningup the vertexof the angleon the centerof the protractorand then usingthe protractor
postulate(see below).Be carefulthough,mostprotractorshavetwo sets of measurements—oneopening
clockwiseand one openingcounterclockwiseMakesure you use the samescalewhenreadingthe measures
of the angle.
ProtractorPostulate:For everyanglethereis a numberbetween0 and 180 that is the measureof the
anglein degrees.You can use a protractorto measurean angleby aligningthe centerof the protractoron
the vertexof the angle.The angle’s measureis then the absolutevalueof the differenceof the numbers
shownon the protractorwherethe sidesof the angleintersectthe protractor.
It is probablyeasierto understandthis postulateby lookingat an example. The basicidea is that you do
not needto start measuringan angleat the zero mark,as long as you find the absolutevalueof the difference