1. Mathematical Justifications
Valid Mathematical Justifications
Are used to support conclusions in a proof or mathematical argument.
They can be…
Definitions
Postulates
Properties
Theorems

2. “Definition of _____________________________”
Congruent:  ↔ =
Bisect: bisect ↔ 
Midpoint: midpoint ↔  segments
Supplementary: supplementary ↔ sum 180
Right angle: rt  ↔ 90

3. Postulates we know… Segment Addition Postulate
Angle Addition Postulate  A B C D  A C B

4. Properties…

5. Linear pair  supplementary
THEN IF
Linear pair  supplementary 1 2
 supplementary
Vertical angles congruent
(Vertical s  ) 1  2
Right angles congruent
(rt. s  )  1 2

6. Reflexive Property of =
Symmetric Property of =

7. Definition of Supplementary
Angle Addition Postulate

8.  ↔ =
Linear Pair → supplementary

9. Addition Property of =
Bisect ↔ 
Vertical s → 

10. Solve for x. 1 2 3 4

11. 1 2 3 4