4.1 Classifying Triangles

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Presentation transcript:

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

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

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

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

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

Example: T S R 3x - 5 x + 7 x - 1 Find x, RS, ST, RT 3x - 5 = x + 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 1 +125 – 10 = 180 angle 1 + 115 = 180 angle 1 = 65 OR

Homework: Put this in your agenda Pg 221 1-37 odd