AMSCO'S Geometry. New York - Rye High School

The Addition and Subtraction Postulates 119Note: We write x y to represent the sum of the angles, x and y, onlyif x and y are adjacent angles.Since AB DE indicates that AB > DE and mABC mDEF indicatesthat ABC DEF, that is, since equality implies congruency, we canrestate the partition postulate in terms of congruent segments and angles.Postulate 3.5.1A segment is congruent to the sum of all its parts.Postulate 3.5.2An angle is congruent to the sum of all its parts.The Addition PostulateThe addition postulate may be stated in symbols or in words as follows:Postulate 3.6If a b and c d, then a c b d.If equal quantities are added to equal quantities, the sums are equal.EXAMPLE 1The following example proof uses the addition postulate.gGiven: ABC and DEF with AB DE and BC EF.Prove: AC DFgA B CD E FProof Statements Reasons1. AB DE 1. Given.2. BC EF 2. Given.3. AB BC DE EF 3. Addition postulate. (Or: If equalquantities are added to equalquantities, the sums are equal.)4. AB BC AC 4. Partition postulate. (Or: A whole isDE EF DFequal to the sum of all its parts.)5. AC DF 5. Substitution postulate.