Chp 3. Proof
The introductory work is done. We can finally commence with proof. Among the results proven: the angles in a linear pair are supplementary, the angles in a vertical pair are equal, and perpendicular lines form four right angles.
We'll also begin our study of indirect proof. Have you ever heard said that you can't prove a negative? That's false. Negatives can be proven, and often those proofs are indirect.
The chapter ends with an assignment named "Two Truths and a Lie". You'll be presented with groups of three statements; in each group, two are true and one is a lie. You'll sketch the object described in GeoGebra and use that sketch to find the lie. My purpose is two-fold: (1) build up your GeoGebra skills, and (2) make you begin to think about polygon congruence which is the topic of the next chapter.
3.1 Conditional Statements
Lecture, PowerPoint, Worksheet
3.2 Proof Structure
Lecture, PowerPoint, Worksheet
3.3 Angle Proofs
Lecture, PowerPoint, Worksheet
3.4 Part Whole Proofs
Lecture, PowerPoint, Worksheet
3.5 Indirect Proof
Lecture, PowerPoint, Worksheet
3.6 Two Truths and a Lie
Pythagoras' Theorem
Lecture, PowerPoint, The Proof
Euclid's Theorem
Lecture, PowerPoint, The Proof
Solutions (also see Selected Proofs)