1. Have your homework out and be in your seat when the bell rings!

2. Intro to Proofs!

3. Given: -5x + 7 + 9x = 52 – x Prove: x = 9
Statements
Reasons
-5x x = 52 – x
Given
4x + 7 = 52 – x
Combining Like Terms
5x + 7 = 52
Addition
5x = 45
Subtraction
x = 9
Division
Q.E.D

4. Symmetric Property
If mA = 80°, then 80° = mA

5. Substitution
If m1 = 30° m1 = m2 then m2 = 30°

6. Given:. 1 ≅3. 1 and 2 are complimentary
Given: 1 ≅3 1 and 2 are complimentary. 3 and 4 are complimentary. Prove: 2 ≅4.
Statements
Reasons
1 ≅3 1 and 2 are complimentary. 3 and 4 are complimentary.
Given
m1 = m3
Definition of Congruent Angles.
m1 + m2 = 90°
m3 + m4 = 90°
Definition of Complimentary Angles
m1 + m2 = m3 + m4
Substitution
m3 + m2 = m3 + m4
m2 = m4
Subtraction
2 ≅4.
Definition of Congruent Angles
Q.E.D.

7. Given: AC ≅ BD Prove: AB ≅ CD
Statements
Reasons
AC ≅ BD
Given
AC = BD
Definition of Congruent Segments.
AC = AB + BC
BD = BC + CD
Segment Addition Postulate
AB + BC = BC + CD
Substitution
AB = CD
Subtraction
AB ≅ CD
Definition of Congruent Segments
Q.E.D.