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- 2D Shapes and Planes

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Get Started Now- Intro Lesson: a3:20
- Intro Lesson: b5:59
- Intro Lesson: c7:54
- Intro Lesson: d4:11
- Lesson: 1a1:11
- Lesson: 1b1:16
- Lesson: 1c1:26
- Lesson: 1d1:25
- Lesson: 1e1:09
- Lesson: 1f1:15
- Lesson: 2a1:47
- Lesson: 2b1:57
- Lesson: 2c1:30
- Lesson: 2d1:08
- Lesson: 2e1:32
- Lesson: 2f1:42
- Lesson: 3a4:27
- Lesson: 3b4:20
- Lesson: 3c4:38
- Lesson: 4a2:21
- Lesson: 4b2:49
- Lesson: 4c4:27
- Lesson: 4d3:52

In this lesson, we will learn:

- How to classify triangles by their side lengths
- How to classify triangles by their angles

- A
**triangle**is a 2-dimensional (2D) shape with__3 straight sides__and__3 angles__ - A triangle’s angles always add up to 180° degrees
**Triangles**can be**classified**in 2 ways:- By their
**side lengths** - By the size of their
**angles** - When looking at
**side lengths**, we classify triangles by__how many sides are the same__length (how many sides are “**congruent**”) - If
__no__sides are the same, it is a**scalene triangle** - If
__two__sides are the same, it is an**isosceles triangle** - If
__all three__sides are the same, it is an**equilateral triangle** - When looking at the
**angles**, we classify triangles by__its biggest angle__and comparing it with the**right angle**(are the angles smaller than, equal to, or greater than 90° degrees?) - If all of the angles are smaller than 90° , it is an
**acute triangle** - If one of the angles is exactly 90° , it is a
**right triangle** - If one of the angles is bigger than 90° , it is an
**obtuse triangle**

- IntroductionIntroduction to Classifying triangles:a)What are the basic characteristics of triangle shapes/polygons?b)How to classify triangles by their side lengthc)How to classify triangles by their anglesd)Review on the six classifications for triangles
- 1.
**Classifying triangles by side lengths**

Classify the triangle by its side lengths. Is it scalene, isosceles, or equilateral?a)

b)

c)

d)

e)

f)

- 2.
**Classifying triangles by angles**

Classify the triangle by its angles. Is it acute, right, or obtuse?a)

b)

c)

d)

e)

f)

- 3.
**Classifying triangles by more than one type**

Classify the triangle by BOTH its side length and angles. (scalene, isosceles, or equilateral; acute, right or obtuse)a)

b)

c)

- 4.
**Word Problems: Classifying Triangles**

Use this figure to answer the following questions:a)If a triangle's side lengths are: 2cm, 1cm, and 1.73cm how would you classify it and why?b)If this triangle is a right triangle, what types of angles does it have?c)Is it possible for this triangle to have an obtuse angle? Why or why not?d)If this right triangle has one angle that is 30°, give the measures of all three of the angles.