1. Geometry
Organising is what you do before you do something, so that when you do it, it is not all mixed up.
A.A. Milne
Today:
Over Proof Intro
2.5 Instruction
Practice

2. 2.5 Postulates and Proofs
Objectives: 1. Justify statements about congruent segments. 2. Write reasons for steps in a proof. Vocabulary: Reflexive, Symmetric, Transitive

3. 2.5 Postulates and Proofs Terminology of Geometry
Theorem: A true statement that follows as a result of other true statements.
Two-column proof: numbered statements and reasons that show the logical order of an argument.

4. 2.5 Postulates and Proofs
Given: HIJK is a rectangle
Prove: HK = 6 6

5. 2.5 Postulates and Proofs Properties of Equality:
Segment Length Angle Measure
Reflexive For any segment AB, For any angle A,
AB = AB mA = mA
Symmetric If AB = CD, then If mA = mB,
CD = AB then, mB = mA
Transitive If AB = CD and If mA = mB
CD = EF then AB = EF and mB = mC, then mA = mC

6. 2.5 Postulates and Proofs
Now have same properties of congruence Reflexive: AB  AB A  A Symmetric: If AB  CD, If A  B, then CD  AB then B  A Transitive: If AB  CD and If A  B and CD  EF, then B  C, then AB  EF A  C

7. 2.5 Postulates and Proofs statements reasons1
Given: m1 = m2 and m3 = m4 Prove: m1 = m4 2 3
statements
reasons 4

8. Geometry
Organising is what you do before you do something, so that when you do it, it is not all mixed up.
A.A. Milne
Assignment:
2.5 p 131: 7, 9, 30 (set it up like in our notes, get as far as you can!), 52