Post on 29-Dec-2015
3-4 PARALLEL LINES AND THE TRIANGLE ANGLE-SUM THEOREMObjectives: 1) to classify triangles and find the measures of their angles2) To use exterior angles of triangles
Watch the Video for the Proof of Triangle Angle-Sum Theorem
Try these. Draw and mark a triangle to fit each description. If no triangle can be drawn, write not possible and explain why.a) acute scalene
b) Isosceles right
c) Obtuse equiangular
• Exterior angle of a polygon: angle formed by a side and an extension of an adjacent side• Remote interior angles: the two nonadjacent interior angles
What is an Isosceles Triangle?
• Isosceles triangle: A triangle with at least two congruent sides • Legs: The congruent sides of an isosceles triangle• Base: The “other” side not counting as the two congruent sides• Vertex angle: The angle included by the two congruent sides• Base angles: The Angles that include the Base
Example 6: Apply Concepts
Triangle RST is an isosceles triangle. • R is the vertex angle, RS = x + 7, ST = x – 1, and RT = 3x – 5. • Find x, RS, ST, and RT.