1. 8-4 Triangles Objective: Students find unknown angles and line segment lengths in triangles.

2. Vocabulary  Acute triangle- has 3 acute angles  Right triangle- has 1 right angle  Obtuse triangle- has 1 obtuse angle  Equilateral triangle- has 3 congruent sides and 3 congruent angles

3. Vocabular y  Isosceles triangle- has at least 2 congruent sides and 2 congruent angles  Scalene triangle- has no congruent sides and no congruent angles  Midpoint- of a segment is the point that divides the segment into 2 congruent segments  Altitude- of a triangle is a perpendicular segment from a vertex of the triangle to the line containing the opposite side

4. Triangle Sum Theorem WordsNumbersAlgebra The interior angle measures of a triangle add to 180º 43º79º 58º 43 + 58 + 79 = 180 rºrº sºsºtº r + s + t = 180

5. Example 1  Find Angles in Acute, Right, or Obtuse Triangles. Find x in the acute triangle 42º 63º xºxº Find x in the right triangle 37º xºxº

6. Example 2  Find the angle measure in the equilateral triangle Finding Angles in Equilateral, Isosceles, or Scalene Triangles. mºmºmºmº mºmº 4pº  Find the angle measure in the scalene triangle 3pº2pº

7. Example 3  Finding the Length of a Line Segment  In the figure, M is the midpoint of PQ and RM is an altitude of △ PQR. Find the length of RM. R PQ 24 m M 20 m

8. Problem #1  Find q in the acute triangle.