1. Splash Screen

2. You solved equations by adding or subtracting. (Lesson 4–3)
Find the missing angle measure of a triangle.
Classify triangles by properties and attributes.
Then/Now

3. line segment
triangle
vertex
congruent
Vocabulary

4. Concept A

5. Find the value of x in ΔDEF.
Find Angle Measures
Find the value of x in ΔDEF.
Write an equation.
x = 180 Substitution
133 + x = 180 Simplify.
133 – x = 180 – Subtract 133 from each side.
x = 47 Simplify.
Answer: x is 47, so mF = 47°.
Example 1

6. Find the value of x in ΔMNO.
B. 123
C. 139
D. 303
Example 1

7. The sum of the angle measures is 180.
Use Algebra to Find Angle Measures
ALGEBRA The measures of the angles of a triangle are 2x, x + 25, and x – 5. What are the measures of the angles?
The sum of the angle measures is 180.
2x + (x +25) + (x + -5) = 180 Write the equation.
4x +20 = 180 Combine like terms.
Subtract.
4x = Simplify.
Divide each side by 4.
x = 40 Simplify.
Example 2

8. Substitute 40 for x in each expression. 2x = 2(40) = 80
Use Algebra to Find Angle Measures
Substitute 40 for x in each expression.
2x = 2(40) = 80
x + 25 = = 65
x - 5 = = 35
Answer: The measures of the angles are 80°, 65°, and 35°.
Example 2

9. Concept B

10. Concept C

11. Concept D

12. A. Classify the triangle below by its angles and by its sides.
Classify Triangles
A. Classify the triangle below by its angles and by its sides.
Angles: The triangle has an obtuse angle.
Sides: The triangle has no congruent sides.
Answer: The triangle is an obtuse scalene triangle.
Example 4

13. B. Classify the triangle by its angles and by its sides.
Classify Triangles
B. Classify the triangle by its angles and by its sides.
Angles: The triangle has a right angle.
Sides: The triangle has two congruent sides.
Answer: The triangle is a right isosceles triangle.
Example 4

14. A. Classify the triangle by its angles and by its sides.
A. right scalene
B. obtuse scalene
C. obtuse isoceles
D. acute equilateral
Example 4 CYP A

15. B. Classify the triangle by its angles and by its sides.
A. right isoceles
B. obtuse isoceles
C. obtuse scalene
D. acute equilateral
Example 4 CYP B

16. Concept D