2.5 Postulates and Paragraph Proofs.notebook Unit 3: Reasoning and Proof 2.5 Postulates and Paragraph Proofs What is a postulate? September 10, 2013 Name Geometry 4B Date a statement about fundamental basics in geometry - accepted as true without proof ex: The intersection of two lines is a point. What is an axiom? a statement accepted as true What is a theorem? a statement we can prove using definitions, postulates and properties ex: x = x ex: Vertical angles are congruent. What is a proof? logical argument used to prove a statement is true 1 2.5 Postulates and Paragraph Proofs.notebook September 10, 2013 p. 127 in your book 2 2.5 Postulates and Paragraph Proofs.notebook September 10, 2013 3 2.5 Postulates and Paragraph Proofs.notebook September 10, 2013 4 2.5 Postulates and Paragraph Proofs.notebook September 10, 2013 Explain Why: If M is the midpoint of XY, then XM = MY. Write your explanation in a short paragraph (2 or 3 sentences) 5 2.5 Postulates and Paragraph Proofs.notebook September 10, 2013 Steps to a Proof: 1) List the given information 2) List the statement you are proving 3) Create an argument (a logical chain of statements from the given info to the statement you are proving) 4) Provide reasons for your statements (definitions, algebraic properties, postulates) 5) State what you have proven 6 2.5 Postulates and Paragraph Proofs.notebook September 10, 2013 This is also in your book on page 129. 7 2.5 Postulates and Paragraph Proofs.notebook September 10, 2013 Homework: LOD and LOS Practice p. 131 # 2729 Write a paragraph proof for: Given: 2 and 4 are vertical angles Prove: 2 4 1 2 3 4 8 2.5 Postulates and Paragraph Proofs.notebook September 10, 2013 9

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