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Section13.2:GeneralAnglesandRadianMeasure
Thissectionisdividedupinto5minilessonsthatwillallfittogetherintheendlikeabigpuzzle.
Youmightfeeloutofyourcomfortzoneforawhile,butstickwithit...andstudy!
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A.AnglesinStandardPosition
Inthelastsection,wejustworkedwithacuteanglesintriangles.
Now,wewillbranchouttoangleswithameasureofanyrealnumber.
Thisrequiressomenewvocabularyterms.
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Wewillstart"mapping"anglesonacoordinateplane.
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Ex.1:Let'sdrawsomeanglesinstandardposition.
a.210
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b.45 c.510
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B.CoterminalAngles
Twoanglesarecoterminaliftheirterminalsidescoincide.
Inthepreviousexample,150and510arecoterminal.
Whatisthenumericrelationshipbetweenthesetwomeasures?
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Ex.2:Findonepositiveandonenegativeanglethatiscoterminalwiththegivenangle.
a.60
b.495
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LearningOpportunityforthissectionsofar:(yes,therewillbemore.)
p.8625#1,3,4,69,14,1518,5561odd
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C.RadianMeasure
Sofar,theonlywayyouhavemeasuredanglesisbydegrees.Youcanmeasureanangleusingaprotractortodetermineitsmeasure.
AnotherwaytomeasureanangleistouseRadianMeasure.Itisawaytomeasureananglebythelengthofitsarc.Intheory,youcouldmeasuretheanglewithatapemeasure(cmorin).
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DefinitionofaRadian:
Oneradianisthemeasureofanangleisstandardpositionwhoseterminalsideinterceptsanarcof
lengthr.
Sowhatdoesthismean?
SMART Notebook
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So,somealgebratounderstandtheconceptofradians:
360 = CircumferenceofaCircle
360 = 2r
Inaunitcircle,wesettheradius=1Therefore
360 = 2radians(Thisisalength)
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a.Sowhatis180inradians?
b.90?
c.45?
Hereisthegeneralwaywecanconvertfromradianstodegreesandviceversa.
RD =
180
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Ex.3:Convertingbetweenradiansanddegrees.
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D.Let'sputthewholelessontogether!
Youneedtobeableto:
Drawanangle(indegreesorradians)instandardposition.
Findpositiveandnegativecoterminalanglesgivenanangleineitherdegreeorradianmeasure
Convertbetweendegreeandradianmeasure
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Ex.4.
a.
Tip:Workwithmeherewiththefractions.Youhavetothinkinradians.
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b. c.
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LearningOpportunity#2:(yes,thereisonemoreminilesson)
p.8625#5,1013,1922,2331
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E.ArcLengthandAreaofaSector
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Ex.5
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FinalLearningOpportunity:
p.863#3238
p.865Quiz1(Toprepareforyour13.113.2Quiznextclass.)
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