Section 3-3 Parallel Lines and the Triangle Angle-Sum Theorem

Section 3-3Parallel Lines and the Triangle Angle-Sum Theorem

1 1 2 3 3 2 Activity #1 1 2 3

1 2 3 1 Activity #2 2 3

2 3 D E Formal Proof A 1 Triangle Angle-Sum Theorem: The sum of the measures of the angles of a triangle is 180˚. 4 5 B C

Formal Proof A Triangle Exterior Angle Theorem: The measure of each exterior angle of a triangle equals the sum of the measures of its two remote interior angles. 2 D 4 1 3 B C

Classify by Angles Classifying Triangles 60˚ 60˚ 60˚ Obtuse Acute Equiangular Right Classify by Sides Equilateral Isosceles Scalene

Example 1 x 67˚ 48˚

Example 2 z 70˚ x y

Example 3:classify by angles and sides 5 2 120˚ 4

Example 4: 125˚ X

Example 5: A triangle with a 90˚ angle has sides that are 3 cm, 4 cm, and 5 cm long. Classify the triangle by its angles and sides.

Example 6: y 70˚ 42˚

Example 7: 90˚ 76˚ x

Example 8: 2x + 28 4x 32˚

Example 9: 5x + 40 10x 3x − 4

Example 10: x 125˚ 160˚

Section 3-3 Parallel Lines and the Triangle Angle-Sum Theorem