Lesson 2-5 Postulates

& Proofs

Proofs

Defined: A way of organizing your thoughts and justifying your reasoning. Proofs use definitions and logic!

Example Proof

Given: You do all your homework

Prove: You will earn a homework pass

Statements Reason

1) You do all your homework 1) Given

2) 100% homework average2) Result of doing ALL your work

3) You earn a homework pass 3) Defined class reward

What can you conclude if GIVEN: Isosceles Triangle: Equilateral Triangle: Perpendicular Lines: Parallel Lines: Midpoint: Complementary Angles: Supplementary Angles:

Example Proof E

F G

Given: F is a right angle

Prove: E & G are complementary

Statements Reason

1) F is a right angle 1) Given

2) F = 90 2) Def. Of Right Angles

3) F + E + G = 180 3) Sum of Angles of 4) 90 + E + G = 180 4) Substitution

5) E + G = 90 5) Subtraction

6) E & G are complementary 6) Definition