1. Splash Screen

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

3. Vocabulary line segment triangle vertex congruent

4. Concept A

5. Example 1 Find Angle Measures 100 + 33 + x =180Substitution 133 + x=180Simplify. 133 – 133 + x=180 – 133 Subtract 133 from each side. x=47Simplify. Answer: x is 47, so m  F = 47°. Find the value of x in ΔDEF. Write an equation.

6. Example 1 A.57 B.123 C.139 D.303 Find the value of x in ΔMNO.

7. Example 2 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? 4x +20 = 180Combine like terms. x = 40Simplify. 2x + (x +25) + (x + -5) = 180Write the equation. The sum of the angle measures is 180. - 20 -20 Subtract. Divide each side by 4. 4x = 160 Simplify.

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

9. Concept B

10. Concept C

11. Concept D

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

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

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

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

16. Concept D