Measure and Classify Angles 1.4 Geometry Angles An angle is created by two rays that have a common endpoint Each ray is called the side of the angle. The common endpoint is called the vertex of the angle. The amount of rotation about the vertex is called the measure of the angle. Common units of measurement of angles are degrees and radians. C A B Parts of an angle C Exterior of angle Interior of angle A B Angles are written with either the vertex point [if no other angles share this vertex] or a point on one of the rays, the vertex, and the point on the other ray. A CAB BAC Types of angles Acute Obtuse Right Straight 0o < acute < 90o 90o < obtuse < 180o right = 90o Straight = 180o Adjacent angles C D O A DOC is adjacent to COA DOA is NOT adjacent to COA Protractor Postulate Each rotation of a ray about a vertex has a unique value between 0 and 180 degrees Angle Addition Postulate C D O A If C is in the interior of AOD, then mAOC + mCOD = mAOD Angle measures mFAB = 90 mEAB = 60 mBAG = 120 mDAB = 45 mBAH = 135 G mBAI = 150 F H D I mBAJ = 180 J mBAC = 30 E C A B