1. Holt McDougal Geometry 4-1 Classifying Triangles Warm Up Classify each angle as acute, obtuse, or right. 1. 2. 3. 4. If the perimeter is 47, find x and the lengths of the three sides. right acute x = 5; 8; 16; 23 obtuse

2. Holt McDougal Geometry 4-1 Classifying Triangles Classify triangles by their angle measures and side lengths. Use triangle classification to find angle measures and side lengths. Today’s Goals!

3. Holt McDougal Geometry 4-1 Classifying Triangles Recall: Triangle - ( ) is a polygon with three sides. Triangles can be classified in two ways:  by their angle measures  by their side lengths.

4. Holt McDougal Geometry 4-1 Classifying Triangles B A C AB, BC, and AC are the sides of ABC. A, B, C are the triangle's vertices.

5. Holt McDougal Geometry 4-1 Classifying Triangles Acute Triangle Three acute angles Triangle Classification By Angle Measures

6. Holt McDougal Geometry 4-1 Classifying Triangles Equiangular Triangle Three congruent acute angles Triangle Classification By Angle Measures

7. Holt McDougal Geometry 4-1 Classifying Triangles Right Triangle One right angle Triangle Classification By Angle Measures

8. Holt McDougal Geometry 4-1 Classifying Triangles Obtuse Triangle One obtuse angle Triangle Classification By Angle Measures

9. Holt McDougal Geometry 4-1 Classifying Triangles Use the figure to classify each triangle by its angle measures. 1.  DFG 2.  DEG 3.  EFG

10. Holt McDougal Geometry 4-1 Classifying Triangles Equilateral Triangle Three congruent sides Triangle Classification By Side Lengths

11. Holt McDougal Geometry 4-1 Classifying Triangles Isosceles Triangle At least two congruent sides Triangle Classification By Side Lengths

12. Holt McDougal Geometry 4-1 Classifying Triangles Scalene Triangle No congruent sides Triangle Classification By Side Lengths

13. Holt McDougal Geometry 4-1 Classifying Triangles Classify each triangle by its side lengths. 1.  EGF 2.  DEF 3.  DFG

14. Holt McDougal Geometry 4-1 Classifying Triangles

15. Holt McDougal Geometry 4-1 Classifying Triangles Remember! When you look at a figure, you cannot assume segments are congruent based on appearance. They must be marked as congruent.

16. Holt McDougal Geometry 4-1 Classifying Triangles Find the side lengths of JKL. Solve for x! Step 1 Find the value of x. JK = KL Notice Congruent Marks 4x – 10.7 = 2x + 6.3 2x = 17.0 x = 8.5 Step 2 Substitute 8.5 into the expressions to find the side lengths. JK = 23.3 KL = 23.3JL = 44.5

17. Holt McDougal Geometry 4-1 Classifying Triangles Find the side lengths of equilateral FGH. FG = GH = FH 3y – 4 = 2y + 3 y = 7 FG = 17 FG = GH = FH = 17

18. Holt McDougal Geometry 4-1 Classifying Triangles Quiz Classify each triangle by its angles and sides. 1. MNQ 2. NQP 3. MNP 4. Find the side lengths of the triangle. acute; equilateral obtuse; scalene acute; scalene 29; 29; 23

19. Holt McDougal Geometry 4-1 Classifying Triangles Assignment P. 219 12-19,23-34