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Chapter 4.1 - Classifying Triangles Objective: To be able to identify and classify triangles by their angles and sides. Check.4.9 Classify triangles, quadrilaterals, and polygons (regular, non-regular, convex and concave) using their properties. Check.4.10 Identify and apply properties and relationships of special figures (e.g., isosceles and equilateral triangles, family of quadrilaterals, polygons, and solids). Classifying Triangles Classify by Angles • Acute Triangle • All angles < 90 • Obtuse Triangle • One angle > 90 Classify by Sides • Scalene Triangle • No two sides are the same • Isosceles Triangle • At least two sides are the same • Equilateral Triangle • Right Triangle • One angle = 90 • All sides are the same Acute Triangles Classify the Triangles A • ADB • EDB Right Triangles B C D • • • • ACD ABC DCE BCE Obtuse Triangles E • ADE • AEB Isosceles Triangles Classify the Triangles A • ADB • EDB Equilateral Triangles • none B C E Scalene Triangles D • AEB • AED • ACB • ACD • BCD • DCE Find Missing Values in Triangle Find x and the measure of each side of the Equilateral Triangle RST if RS = x + 9, ST = 2x, and RT = 3x -9 S x+9 R x + 9 = 2x -x -x 9 =x 2x 3x - 9 T RS = x + 9 =9+9 = 18 Find Missing Values in Triangle Find d and the measure of each side of the Equilateral Triangle KLM if KL = d + 2, LM = 12 - d, and KM = 4d -13 L d+2 K 12 - d 4d -13 M d + 2 = 12 - d +d +d 2d + 2 = 12 -2 -2 2d = 10 d=5 KL = d + 2 =5+2 =7 Use the distance formula • Find x and the measure of the sides of DEC. Classify the triangle by its sides E(-5, 3) C (3, 9) D (2, 2) C E D • Isosceles Triangle Use the distance formula • Find x and the measure of the sides of RST. Classify the triangle by its sides R(-1, -3) S (8, -1) T (4, 4) T R • Scalene Triangle S RS = √85 ST= √41 RT= √74 Practice Assignment • Block Page 239, 16 – 36 Every 4th and 44 • Honors page 239 30 – 52 Even