1. Triangles and Angles Classifying Triangles

2. Triangle Classification by Sides Equilateral 3 congruent sides Isosceles 2 congruent sides Scalene No congruent sides

3. Triangle Classification by Angles Equilateral 3 congruent angles Acute 3 acute angles Obtuse 1 obtuse angle Right 1 right angle 60 80 40 70 120 40 20 90 35 55

4. More Definitions Interior Angles: angles inside the triangle Interior Angles: angles inside the triangle (angles A, B, and C) (angles A, B, and C) A B C 1 2 3 Exterior Angles: angles adjacent to the interior angles Exterior Angles: angles adjacent to the interior angles (angles 1, 2, and 3) (angles 1, 2, and 3)

5. Triangle Sum Theorem The sum of the measures of the interior angles of a triangle is 180 o. The sum of the measures of the interior angles of a triangle is 180 o. A B C <A + <B + <C = 180 o <A + <B + <C = 180 o When you add all the angles of a triangle together, you get the number 180. 60 60 + 60 + 60 = 180 o 60 + 60 + 60 = 180 o 40 80 40 40 + 80 + 40 = 180 o 40 + 80 + 40 = 180 o 30 100 50 30 + 100 + x = 180 o 30 + 100 + x = 180 o

6. Solving for The Angles Write the angles with addition signs in between them. Write = 180 Combine Like Terms Solve for x Substitute x back in if you need to. A B C 92 42 x 92 + 42 + x = 180 92 + 42 + x = 180 134 + x = 180 134 + x = 180 -134 -134 -134 -134 X=46 X=46 Write the angles with addition signs in between them. Write the angles with addition signs in between them. Write = 180 Write = 180 Combine Like Terms Combine Like Terms Solve for x Solve for x Substitute x back in if you need to. Substitute x back in if you need to.