CK12 - Trigonometry

We can also measurethe rotationin degrees.In the previouslessonwe workedwith anglesin triangles,
measuredin degrees.You may recallfrom geometrythat a full rotationis 360 degrees,usuallywrittenas

360
o

. Half a rotationis then 180
o
and a quarterrotationis 90
o
. Eachof thesemeasurementswill be important
in this lesson,as well as in the remainderof the chapter.

Acute,Right,Obtuse,and StraightAngles

In general,anglesare categorizedby their size.The tablebelowsummarizesthe categories,whichmight
be familiarfrom the previouslesson.

Name Description

Acute An anglewhosemeasureis less than 90 degrees

Right An anglewhosemeasureis exactly90 degrees

Obtuse An anglewhosemeasureis morethan 90 degrees,but less than 180 degrees.

Straight An anglewhosemeasureis exactly180 degrees

You shouldmakesure that you can visuallydeterminewhichcategoryan anglebelongsto.

Example1:Determineif the angleis acute,right,obtuse,or straight.

a. b. c.

Solution:

a. This angleis an acuteangle

If it is difficultto categorizethe anglevisually, you can compareit to a right angle.Doingthis will help you
see that the angleis smallerthan a right angle.