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

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Presentation transcript:

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

Activity #

Activity #

Formal Proof 1 A B C DE Triangle Angle-Sum Theorem: The sum of the measures of the angles of a triangle is 180 ˚.

Formal Proof 2 A B C 13 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. D4

Classifying Triangles Classify by Angles 60 ˚ Equiangular Acute Right Obtuse Classify by Sides EquilateralIsoscelesScalene

Example 1 67 ˚ 48 ˚ x

Example 2 x z y 70 ˚

Example 3 :classify by angles and sides ˚ 5

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: 70 ˚ 42 ˚ y

Example 7: 90 ˚ 76 ˚ x

Example 8: 2x ˚ 4x

Example 9: 5x x 3x − 4

Example 10: x 160 ˚ 125 ˚