AMSCO'S Geometry. New York - Rye High School

Classifying Angles According to Their MeasuresRays and Angles 17Acute AngleRight AngleObtuse AngleStraight AngleGCJH IB AK L D E FDEFINITIONAn acute angle is an angle whose degree measure is greater than 0 and lessthan 90.In the figure above, GHI is an acute angle.DEFINITIONA right angle is an angle whose degree measure is 90.In the figure above, ABC is a right angle. Therefore, we know thatmABC 90. The symbol – | at B is used to show that ABC is a right angle.DEFINITIONAn obtuse angle is an angle whose degree measure is greater than 90 and lessthan 180.In the figure above, JKL is an obtuse angle.A straight angle, previously defined as the union of opposite rays, is an anglewhose degree measure is 180. In the figure above, DEF is a straight angle. Thus,mDEF 180. Note that ED h and EF h, the sides of DEF, are opposite raysand form a straight line.EXAMPLE 1D is a point in the interior of ABC,mABD 15, and mDBC 90.a. Find mABC.b. Name an acute angle.c. Name a right angle.A Dd. Name an obtuse angle.B C