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# 8.2 classifying triangles 1

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### 8.2 classifying triangles 1

1. 1. Lesson 8.2 , For use with pages 411-415 Find the complement and supplement to the angle. 1. 38º 2. 70º
2. 2. Lesson 8.2 , For use with pages 411-415 Find the complement and supplement to the angle. 1. 38º 2. 70º Complement 20º Complement 52º Supplement 142º Supplement 110º
3. 3. 8.2 Classifying Triangles
4. 4. Essential Questions <ul><li>Why is it important to be able to identify congruent triangles in everyday life? </li></ul><ul><li>Where in real life can you use the properties of isosceles and equilateral triangles? </li></ul><ul><li>How are the relationships between lines and planes used in the real world? </li></ul><ul><li>What areas in the real world are properties of parallel lines important? </li></ul>
5. 5. <ul><li>Triangle: a closed figure with three sides made with line segments. </li></ul>
6. 6. Triangles- Classifying by Angles <ul><li>Acute – 3 acute angles </li></ul><ul><li>Right – has one right angle </li></ul><ul><li>Obtuse – has one obtuse angle </li></ul>
7. 7. Triangles- Classifying by Sides <ul><li>Equilateral – 3 congruent sides </li></ul><ul><li>Isosceles – at least 2  sides </li></ul><ul><li>Scalene – no  sides, no  angles </li></ul><ul><li>Are all equilateral triangles isosceles? </li></ul><ul><li>Are all isosceles equilateral? </li></ul>
8. 8. Triangles <ul><li>Triangles can also be classified by the size of angles. </li></ul><ul><ul><li>Yes – this would be a RIGHT triangle, with one 90 degree angle. </li></ul></ul><ul><li>For example: </li></ul>Triangles can be classified by sides. This is a isosceles.
9. 9. <ul><li>Triangles can also be classified by the size of angles. </li></ul><ul><li>Obtuse Triangle – named for its ONE obtuse angle. A triangle can AT MOST one obtuse angle. WHY? </li></ul>Triangles can be classified by sides. This is a scalene.
10. 10. <ul><li>Triangles can also be classified by the size of angles. </li></ul><ul><ul><li>Acute Triangle – named for its THREE ACUTE angles. </li></ul></ul>Triangles can be classified by sides. This is a equilateral.
11. 11. TRIANGLES Isosceles Equilateral Scalene
12. 12. Triangles <ul><li>One common characteristic of triangles is that they ALL have 180 degrees in the sum of the three angles – regardless of size and shape. </li></ul>
13. 13. Triangles <ul><li>So if you know the measurement of 2 angles, you can always find the 3 rd angle. </li></ul>90 ° 30 ° X ° °
14. 14. Triangles 85 ° 61 ° x °
15. 15. Can the angles of a triangle have the given measures? <ul><li>41°, 52°, 87° </li></ul><ul><li>Yes, because they add up to 180°. </li></ul>
16. 16. Can the angles of a triangle have the given measures? <ul><li>38.2°, 49.7°, 92.2° </li></ul><ul><li>No, because they add up to 180.1°. </li></ul>
17. 17. Homework <ul><li>Page 413 #1-22, 29-31 </li></ul><ul><ul><li>Use pencil </li></ul></ul>