Lesson 10-4 Pages Triangles

What you will learn! How to identify and classify triangles.

Triangle Congruent segments Acute triangle Scalene triangle Right triangle Isosceles triangle Obtuse triangle Equilateral triangle

What you really need to know! A triangle is 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: 1. An acute triangle has three acute angles. 2. An obtuse triangle has one obtuse angle. 3. A right triangle has one right angle.

Triangles can also be classified by the lengths of their sides: 1. In a scalene triangle, all sides have different lengths. 2. An isosceles triangle has at least two congruent sides. 3. An equilateral triangle has all three sides congruent.

What you really need to know! Sides that are the same length are congruent segments and are often marked by tick marks.

Example 1: An airplane has wings that are shaped like triangles. Find the missing measure.

= – 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  A + m  B m  A = 50° m  B = 50°

Example 3: Classify the triangle by its angles and by its sides. O btuse Isosceles 30° 120°

Example 4: Classify the triangle by its angles and by its sides. Acute Scalene 80° 70° 30°

Page 430 Guided Practice #’s 3-7

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Homework: Page #’s 8-24 all #’s all Lesson Check 10-4

Page 588 Lesson 10-4