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8-4 Triangles Objective: Students find unknown angles and line segment lengths in triangles. Vocabulary Acute Right triangle- has 3 acute angles triangle- has 1 right angle Obtuse triangle- has 1 obtuse angle Equilateral triangle- has 3 congruent sides and 3 congruent angles 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 Triangle Sum Theorem Words The interior angle measures of a triangle add to 180º Numbers Algebra 58º 79º rº 43º 43 + 58 + 79 = 180 tº sº r + s + t = 180 Example 1 Find Angles in Acute, Right, or Obtuse Triangles. Find x in the acute triangle 42º 63º xº Find x in the right triangle xº 37º Example 2 Finding Angles in Equilateral, Isosceles, or Scalene Triangles. Find the angle measure in the equilateral triangle mº mº mº Find the angle measure in the scalene triangle 4pº 3pº 2pº Example 3 Finding In the Length of a Line Segment the figure, M is the midpoint of PQ and RM is an altitude of △ PQR. Find the length of R RM. 20 m P Q M 24 m Problem #1 Find q in the acute triangle.
