1. Sum of Angles in Triangles

2. Triangles classified by sides A scalene triangle has no congruent sides. An isosceles triangle has at least 2 congruent sides An equilateral triangle, all of the sides are congruent.

3. Triangles classified by angles In an acute triangle, all of the angles are acute. An obtuse triangle has one obtuse angle. A right triangle has one right angle.

4. Classify each triangle according to its sides and angles. EX1) Two congruent sides acuteThree acute angles This is an acute isosceles triangle. EX2) No congruent sides rightOne right angle This is a right scalene triangle. isosceles scalene

5. EX3) Three congruent sides acuteThree acute angles EX4) No congruent sides rightOne right angle equilateral scalene EX5) Two congruent sides obtuse One obtuse angle EX6) Two congruent sides rightOne right angle isosceles

6. Tear off the corners of your triangle and put them together. The sum of the measures of the angles in a triangle is 180 °. m  1 + m  2 + m  3 = 180 ° 1 3 2

7. Find the measure of the unknown angle. 55° 80° x 80° + 55° + x = 180° 135° + x = 180° –135° x = 45° The sum of the measures of the angles is 180°. EX7) 90° + 2x + x = 180° 90° + 3x = 180° –90° 3x = 90° 90° x 2x EX8) 3 = 3 x = 30° 2x = 60°

8. Assignment Page 613 1-16

9. notes

10. Classify Triangles Classify triangles by the lengths of their sides and their angles. Date ______________

11. Triangles classified by sides A scalene triangle An isosceles triangle An equilateral triangle,

12. Triangles classified by angles In an acute triangle An obtuse triangle has A right triangle

13. Classify each triangle according to its sides and angles. EX1) EX2)

14. EX3) EX4) EX5) EX6)

15. Find the measure of the unknown angle. 55° 80° x EX7)

16. 90° 30° x EX8)