1. 4.1 Classifying Triangles
To identify the parts of triangles and classify triangles by their parts

2. Definition
Polygon-closed figure made up of segments (a.k.a sides) that intersect only at their endpoints (a.k.a vertices)

3. Classifying triangles by its angles
Acute- All angles < 90o
Obtuse- One angle > 90o
Right- One angle = 90o
Equiangular- all angles are congruent

4. Classifying Triangles by its sides and/or angles
Scalene- no 2 sides are congruent
Isosceles- 2 sides are congruent
2 base angles congruent
Equilateral- all sides and angles congruent

5. Theorems
Triangle Sum Thm~ The sum of the measures of the interior angles of a triangle is 180.
Exterior Angle Thm~ The measures of an exterior angle of a triangle is equal to the sum of the measures of the two remote nonadjacent interior angles 3 2 1
1 + 2 = 3

6. Example: T S R 3x - 5 x + 7 x - 1 Find x, RS, ST, RT 3x - 5 = x + 7

7. Example Find the measure of angle 1 3x + 40 = 5x – 10 (ext angle thm)
40 = 2x – 10 (subtraction)
50 = 2x (addition)
25 = x (division)
40 + 3(25) + angle 1 = 180
115 + angle 1 = 180
Angle 1 = 65
angle 1 + 5(25) – 10 = 180
angle – 10 = 180
angle = 180
angle 1 = 65 OR

8. Homework:
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