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Learn to classify triangular support beams by sides and angles. Identify types of triangles and determine right angles in coordinates.
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Support Beams Classify the triangular shape of the support beams in the diagram by its sides and by measuring its angles. EXAMPLE 1 Classify triangles by sides and by angles SOLUTION The triangle has a pair of congruent sides, so it is isosceles. By measuring, the angles are 55° , 55° , and 70° . It is an acute isosceles triangle.
Classify PQOby its sides. Then determine if the triangle is a right triangle. Use the distance formula to find the side lengths. STEP1 2 2 – – ( ( ) ) OP = + + 2 2 – – ( ( ) ) y x x y y y x x 2 1 2 2 2 1 1 1 2 2 ( – ( ) (– 1 ) ) 0 2 – 0 2.2 + = = 5 OQ = 2 2 ( – ( ) 6 ) 0 – 0 3 6.7 + = = 45 EXAMPLE 2 Classify a triangle in a coordinate plane SOLUTION
PQ = 2 2 ( – ) 6 (– 1 ) ) 3 – ( 2 7.1 + = = Check for right angles. STEP2 The slope ofOPis 2 – 0 3 – 0 1 . – 2. The slope ofOQis = = – 2 – 0 2 6 – 0 1 – 2 The product of the slopes is – 1 , = 2 – ( ) 2 + 2 – ( ) so OPOQand POQ is a right angle. y x x y 2 2 1 1 50 ANSWER Therefore, PQOis a right scalene triangle. EXAMPLE 2 Classify a triangle in a coordinate plane
Draw an obtuse isosceles triangle and an acute scalene triangle. B A C Q obtuse isosceles triangle R P acute scalene triangle for Examples 1 and 2 GUIDED PRACTICE
Triangle ABChas the vertices A(0, 0), B(3, 3), and C(–3, 3). Classify it by its sides. Then determine if it is a right triangle. Use the distance formula to find the side lengths. STEP1 2 2 – – ( ( ) ) AB = + + 2 2 – ( ( ) ) x x y y y x y x 1 1 2 2 1 2 1 2 2 2 ( – ( ) ( 3 ) ) 0 3 – 0 4.2 + = = 18 BC = 2 2 ( – ( ) –3 ) 3 – 3 3 20 + = = 400 for Examples 1 and 2 GUIDED PRACTICE SOLUTION
AC = 2 2 ( – ) (–3 0 ) ) 3 – ( 0 4.2 + = = 18 Check for right angles. STEP2 3 – 0 3 – 0 The slope ofABis . 1. The slope ofACis = – 1 = – 3 – 0 3 – 0 1(– 1) The product of the slopes is – 1 , = 2 – ( ) + 2 – ( ) so ABACand BAC is a right angle. x y x y 2 1 2 1 Therefore, ABCis a right Isosceles triangle. ANSWER for Examples 1 and 2 GUIDED PRACTICE