Section 2.4: Reasoning with Properties from Algebra

Algebraic Properties of Equality Properties are used to explain why certain steps are being taken, such as in solving an algebra equation. Let a, b, and c be real numbers. Addition Property of Equality If a = b, then a + c = b + c Subtraction Property of Equality If a = b, then a - c = b – c Multiplication Property of Equality If a = b, then ac = bc Division Property of Equality If a = b and c ≠ 0, then a ÷ c = b ÷ c Reflexive Property of Equality For any real number a, a = a Symmetric Property of Equality If a = b, then b = a Transitive Property of Equality If a = b and b = c, then a = c Substitution Property of Equality If a = b, then a can be substituted for b in any equation or expression Distributive Property For any real number, a(b + c) = ab + ac

More Properties of Equality Used in Geometry We can also use the algebraic properties of equality in geometry. PROPERTIES OF LENGTH AND MEASURE Segment Length Angle Measure Reflexive For any segment AB, AB = AB For any angle A, m<A = m<A Symmetric If AB = CD, then CD = AB If m<A = m<B, then m<B = m<A Transitive If AB = CD and CD = EF, then AB = EF If m<A = m<B and m<B = m<C, then m<A = m<C