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Lesson 10-4 Pages 428-431. Triangles. What you will learn!. How to identify and classify triangles. Vocabulary. What you really need to know!.
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Lesson 10-4Pages 428-431 Triangles
What you will learn! How to identify and classify triangles.
What you really need to know! A triangleis a figure with three sides and three angles. The sum of the measures of the angles of a triangle is 180. You can use this to find a missing angle measure in a triangle.
Triangles can be classified by • the measures of their angles: • An acute triangle has three acute angles. • An obtuse triangle has one obtuse angle. • A right triangle has one right angle.
Triangles can also be classified • by the lengths of their sides: • In a scalene triangle, all sides have different lengths. • An isosceles triangle has at least two congruent sides. • An equilateral triangle has all three sides congruent.
What you really need to know! Sides that are the same length are congruent segmentsand are often marked by tick marks.
Example 1: An airplane has wings that are shaped like triangles. Find the missing measure.
112 + 47 = 159 180 – 159 = 21 21°
Example 2: Find m A in ∆ABC if m A = m B and m C = 80°. 180 = m A + m B + m C
180 = m A + m B + m C 180 = m A + m B + 80 100 = m A + m B 100 = 50 + 50 m A = 50°m B = 50°
Example 3: Classify the triangle by its angles and by its sides. 120° 30° 30° Obtuse Isosceles
Example 4: Classify the triangle by its angles and by its sides. 70° 80° 30° Acute Scalene
Page 430 Guided Practice #’s 3-7
Read: Pages 428-429 with someone at home and study examples!
Homework: Page 430-431 #’s 8-24 all #’s 27-34 all Lesson Check 10-4
Page 588 Lesson 10-4