1. Triangles can be classified based on their sides as isosceles, scalene, or equilateral. The sum of the interior angles of any triangle is always 180 degrees. 2. The measure of an exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles. 3. True or false questions about triangle properties include: if two angles are congruent then the third must be; each angle of an equiangular triangle is 60 degrees; a triangle can have at most one right or obtuse angle.

1. Triangular Shape Electromagnetism The Lost Continent of Atlantis Portal to Another Dimension

2. TRIANGLES

4. Thesegments are called the sides.vertex side side vertex vertex side

5. Naming a Triangle and its parts Triangle ABC / ΔABC Angles: A, B, & C Sides: AB, BC, & CA a, b, & c B c a A C b Note: Naming = Consecutive vertices (preferably clockwise)

6. Triangle Classification (accdg. to sides) pg 129 ISOSCELES At least 2 sides congruent SCALENE No sides congruent EQUILATERAL All sides congruent Using the Geoboards

7. Triangle Classification (accdg. to angles) pg 129 ACUTE 3 acute angles RIGHT 1 right angle ┌ EQUIANGULAR All angles congruent OBTUSE 1 obtuse angle

8. Paper-folding Investigation B Draw a triangle similar in shape to the ΔABC. Cut it out. Slide point A along AC toward point C until the fold passes through point B. The crease intersects AC at point D. Unfold the triangle. A C B C D A B A C D

10. Bring points B and C to point D and crease.B A C D B A C D What appears to be true about the sum of the measures of these angles three angles?

11. pg 110 - 111 The sum of the measures of angles of a triangle is 180o. B 4 5 3 B A C 1 2 A C A + B + C = 180o

12. Sample Problems The angles of a triangle are in a ratio 3:4:5. Find the measures of all the angles. 2. pg 111 - 112 (2x)o (4x-8)o (5x-10)o

13. TRUE or FALSE? pg 114 If two angles of one triangle are congruent to two angles of a second triangle, then the third angles are congruent. Each angle of an equiangular triangle measures 60o. In a triangle, there can be at most one right triangle, or at most one obtuse angle. The acute angles of a right triangle are complementary.

14. Exterior Angles of a Triangle pg 116 - 117 ΔABC has been extended to form exterior angles: 1, 2, & 3. Each exterior angle has an adjacent interior angle and two remote interior angles. Example: Exterior angle: Adjacent interior angle: Two remote angles: A 1 6 3 4 5 B C 2 2 4 6 & 5

15. Protractor investigation (exterior and remote interior angles) The measure of an exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles. 1 = 4 + 5 2 = 5 + 6 3 = 4 + 6 pg 117 A 5 1 6 4 3 4 5 B C 2

16. Sample Problems: Solve for x. 1. 2. pg 117 40o xo 23o 84o 7xo 5xo