# Geometry 2.5: Using Postulates and Diagrams

REVIEW: 1&2: Draw a conclusion and name the Law.

1. All stores sell something. Toys R Us is a store.

2. If Miles has money, then he can buy food. If Miles buys food, then he buys a sandwich.

#3 Write in if-then form, and then determine the truth value. If false, state a counterexample.

## 3a)

All dogs have fleas.

3b) converse

#3c) inverse

#3d) contrapositive

Extra Review a) Given this TRUE conditional, write another true statement: If I'm sick, then I won't be there.

Extra Review b) Given this TRUE conditional, write another false statement. If the lights are not off, then it is not dark.

Use the applet below to confirm these postulates: Postulate 2.1   Through any two points there exists exactly one line.Postulate 2.2   Through any three noncollinear points there exists exactly one plane. (Remember to move the diagram around to look at the figure.) *Can you draw a line through G and E? *Can you draw a line through G, A, and C? *Can you draw a line through G, F, and D? >Can you draw a plane through E, F, and D? >Can you draw a plane through G, C, and E? >Can you draw a plane through B, A, and C? (GeoGebra has trouble here...why?) >Can you draw a plane through E, B, A, and C? (You'll have to choose 3 of the points to use .) >Can you draw a plane through E, A, G, and C?