AMSCO'S Geometry. New York - Rye High School

More Angle Definitions 195. For the figure shown:a. Name angle 1 in four other ways.b. Name angle 2 in two other ways.c. Name angle 3 in two other ways.d. Name the point of intersection of AC and BD.e. Name two pairs of opposite rays.f. Name two straight angles each of which has its vertex at E.g. Name two angles whose sum is ABC.AD12E3BC1-6 MORE ANGLE DEFINITIONSCongruent AnglesDEFINITIONCongruent angles are angles that have the same measure.CFBAEDIn the figures, ABC and DEF have the same measure. This is written asmABC mDEF. Since congruent angles are angles that have the samemeasure, we may also say that ABC and DEF are congruent angles, symbolizedas ABC DEF. We may use either notation.ABC DEF The angles are congruent.mABC mDEF The measures of the angles are equal.Note: We do not write ABC DEF. Two angles are equal only if they namethe union of the same rays. For example, ABC CBA.When two angles are known to be congruent, we may mark each one withthe same number of arcs, as shown in the figures above, where each angle ismarked with a single arc.