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Download triangle - Maples Elementary School
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4-1 Classifying Triangles Objectives •Classify triangles by their angle measures and side lengths. •Use triangle classification to find angle measures and side lengths. Holt Geometry 4-1 Classifying Triangles Vocabulary acute obtuse acute triangle equiangular triangle right triangle obtuse triangle equilateral triangle isosceles triangle scalene triangle Holt Geometry 4-1 Classifying Triangles 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. Holt Geometry 4-1 Classifying Triangles C A B AB, BC, and AC are the sides of A, B, C are the triangle's vertices. Holt Geometry ABC. 4-1 Classifying Triangles Triangle Classification By Angle Measures Acute Triangle Three acute angles Holt Geometry 4-1 Classifying Triangles Triangle Classification By Angle Measures Equiangular Triangle Three congruent acute angles Holt Geometry 4-1 Classifying Triangles Triangle Classification By Angle Measures Right Triangle One right angle Holt Geometry 4-1 Classifying Triangles Triangle Classification By Angle Measures Obtuse Triangle One obtuse angle Holt Geometry 4-1 Classifying Triangles Example 1A: Classifying Triangles by Angle Measures Classify BDC by its angle measures. B is an ______ angle. So BDC is an _______ triangle. ADC is a ________ triangle. Holt Geometry 4-1 Classifying Triangles Example 1B: Classifying Triangles by Angle Measures Classify ABD by its angle measures. ABD and CBD form a linear pair, so they are _______________. Therefore mABD + mCBD = ____°. By substitution, mABD + 100° = 180°. So mABD = ____°. ABD is an ______ triangle by definition. Holt Geometry 4-1 Classifying Triangles Triangle Classification By Side Lengths Equilateral Triangle Three congruent sides Holt Geometry 4-1 Classifying Triangles Triangle Classification By Side Lengths Isosceles Triangle At least two congruent sides Holt Geometry 4-1 Classifying Triangles Triangle Classification By Side Lengths Scalene Triangle No congruent sides Holt Geometry 4-1 Classifying Triangles Remember! When you look at a figure, you cannot assume segments are congruent based on appearance. They must be marked as congruent. Holt Geometry 4-1 Classifying Triangles Example 2A: Classifying Triangles by Side Lengths Classify EHF by its side lengths. From the figure, is ________. Holt Geometry . So HF = ____, and EHF 4-1 Classifying Triangles Example 2B: Classifying Triangles by Side Lengths Classify EHG by its side lengths. By the Segment Addition Postulate, EG = __ + __ = 10 + 4 = 14. Since no sides are congruent, EHG is ________. Holt Geometry 4-1 Classifying Triangles Example 3: Using Triangle Classification Find the side lengths of Holt Geometry JKL. 4-1 Classifying Triangles Example 4: Application A steel mill produces roof supports by welding pieces of steel beams into equilateral triangles. Each side of the triangle is 18 feet long. How many triangles can be formed from 420 feet of steel beam? Holt Geometry 4-1 Classifying Triangles Lesson Quiz Classify each triangle by its angles and sides. 1. MNQ 2. NQP 3. MNP 4. Find the side lengths of the triangle. Holt Geometry
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