1. Splash Screen

2. Five-Minute Check (over Lesson 4–1) CCSS Then/Now New Vocabulary
Theorem 4.1: Triangle Angle-Sum Theorem
Proof: Triangle Angle-Sum Theorem
Example 1: Real-World Example: Use the Triangle Angle-Sum Theorem
Theorem 4.2: Exterior Angle Theorem
Proof: Exterior Angle Theorem
Example 2: Real-World Example: Use the Exterior Angle Theorem
Corollaries: Triangle Angle-Sum Corollaries
Example 3: Find Angle Measures in Right Triangles
Lesson Menu

3. Classify ΔRST . A. acute B. equiangular C. obtuse D. right
5-Minute Check 1

4. Find y if ΔRST is an isosceles triangle with RS  RT.
___
A. 8
B. 10
C. 12
D. 14
5-Minute Check 2

5. Find x if ΔABC is an equilateral triangle.
5-Minute Check 3

6. A. ΔABC
B. ΔACB
C. ΔADC
D. ΔCAB
5-Minute Check 4

7. Classify ΔMNO as scalene, isosceles, or equilateral if MN = 12, NO = 9, and MO = 15.
A. scalene
B. isosceles
C. equilateral
5-Minute Check 5

8. Which is not a classification for ΔFGH?
A. acute
B. scalene
C. isosceles
D. equiangular
5-Minute Check 6

9. G.CO.10 Prove theorems about triangles. Mathematical Practices
Content Standards
G.CO.10 Prove theorems about triangles.
Mathematical Practices
1 Make sense of problems and persevere in solving them.
3 Construct viable arguments and critique the reasoning of others.
CCSS

10. You classified triangles by their side or angle measures.
Apply the Triangle Angle-Sum Theorem.
Apply the Exterior Angle Theorem.
Then/Now

11. remote interior angles flow proof corollary
auxiliary line
exterior angle
remote interior angles
flow proof
corollary
Vocabulary

12. Concept 1

13. Concept 2

14. Use the Triangle Angle-Sum Theorem
SOFTBALL The diagram shows the path of the softball in a drill developed by four players. Find the measure of each numbered angle.
Example 1

15. Find the measure of 3.
A. 95
B. 75
C. 57
D. 85
Example 1

16. Concept 4

17. GARDENING Find the measure of FLW in the fenced flower garden shown.
Use the Exterior Angle Theorem
GARDENING Find the measure of FLW in the fenced flower garden shown.
Example 2

18. The piece of quilt fabric is in the shape of a right triangle
The piece of quilt fabric is in the shape of a right triangle. Find the measure of ACD.
A. 30
B. 40
C. 50
D. 130
Example 2

19. Concept 5

20. Find the measure of each numbered angle.
Find Angle Measures in Right Triangles
Find the measure of each numbered angle.
Example 3

21. Find m3.
A. 50
B. 45
C. 85
D. 130
Example 3