Section 2.1 – An Introduction to Proofs

A proof is a convincing argument that something is true.

A proof starts with things that are agreed on or accepted as true. These are called postulates (or axioms). Then logic is used to reach a conclusion.

Formal Proofs – proofs that follow a prescribed form

5x + 4 = 24 Given

5x = 20 Subtraction Property of Equality

x = 4 Division Property of Equality

Each statement on the left is given justification in the column on the right.

Styles of Proofs

• Two-column proofs
• Paragraph proofs
• Flowchart proofs
• Coordinate proofs
• Table proofs