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Objective Classify triangles by their angle measures and side lengths. Recall that a triangle ( ) is a polygon with three sides. Triangles can be classified in two ways: by their angle measures or by their side lengths. Classify by angle measure Acute Has three acute angles Right Has one right angle Obtuse Has one obtuse angle Equiangular All angles are congruent Classify by Sides Equilateral All sides congruent Isosceles At least two sides congruent Scalene No sides congruent Parts of an isosceles triangle Vertex Leg Leg Base Angle Base Base Angle Remember! When you look at a figure, you cannot assume segments and angles are congruent based on appearance. They must be marked as congruent. Example Classify ACD by its side lengths. From the figure, scalene. . So AC = 15, and ACD is Example Classify FHG by its angle measures. EHG is a right angle. Therefore mEHF +mFHG = 90°. By substitution, 30°+ mFHG = 90°. So mFHG = 60°. FHG is an equiangular triangle by definition. Example Classify BDC by its angle measures. B is an obtuse angle. B is an obtuse angle. So triangle. BDC is an obtuse Homework Section 3 – 2 # 1-21 all, 22-34 even