1. Use algebra to write two-column proofs.
Use properties of equality to write geometric proofs.
Splash Screen

2. Preparation for G.CO.9 Prove theorems about lines and angles.
Content Standards
Preparation for G.CO.9 Prove theorems about lines and angles.
Mathematical Practices
3 Construct viable arguments and critique the reasoning of others.
CCSS

3. algebraic proof
two-column proof
formal proof
Vocabulary

4. Vocabulary

5. Concept

6. Justify Each Step When Solving an Equation
Solve 2(5 – 3a) – 4(a + 7) = 92.
Example 1

7. Solve –3(a + 3) + 5(3 – a) = –50.
Example 1

8. Write an Algebraic Proof
Example 2

9. Write an Algebraic Proof
Statements Reasons
Proof:
Example 2

10. Which of the following statements would complete the proof of this conjecture?
If the formula for the area of a trapezoid is , then the height h of the trapezoid is given by
Example 2

11. Statements Reasons
Proof:
Example 2

12. Write a Geometric Proof
If A B, mB = 2mC, and mC = 45, then mA = 90. Write a two-column proof to verify this conjecture.
Example 3

13. Write a Geometric Proof
Statements Reasons
Proof:
Example 3

14. Example 3

15. 3. Definition of congruent segments
Statements Reasons
Proof:
1. Given 1. 2.
2. _______________ ?
3. AB = RS
3. Definition of congruent segments
4. AB = 12
4. Given
5. RS = 12
5. Substitution
Example 3

16. Homework
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Vocabulary