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Ch 5: Basic Geometry: Triangles

About This Chapter

The Basic Geometry: Triangles chapter of this Basic Geometry: Help & Review course is the simplest way to master triangles. This chapter uses simple and fun videos that are about five minutes long, plus lesson quizzes and a chapter exam to ensure you learn the essentials of triangles.

Who's It For?

Anyone who needs help learning or mastering triangles material will benefit from the lessons in this chapter. There is no faster or easier way to learn about triangles. Among those who would benefit are:

  • Students who have fallen behind in understanding triangles
  • Students who struggle with learning disabilities or learning differences, including autism and ADHD
  • Students who prefer multiple ways of learning math (visual or auditory)
  • Students who have missed class time and need to catch up
  • Students who need an efficient way to learn about triangles
  • Students who struggle to understand their teachers
  • Students who attend schools without extra math learning resources

How It Works:

  • Find videos in our course that cover what you need to learn or review.
  • Press play and watch the video lesson.
  • Refer to the video transcripts to reinforce your learning.
  • Test your understanding of each lesson with short quizzes.
  • Verify you're ready by completing the Basic Geometry: Triangles chapter exam.

Why It Works:

  • Study Efficiently: Skip what you know, review what you don't.
  • Retain What You Learn: Engaging animations and real-life examples make topics easy to grasp.
  • Be Ready on Test Day: Use the Basic Geometry: Triangles chapter exam to be prepared.
  • Get Extra Support: Ask our subject-matter experts any triangles question. They're here to help!
  • Study With Flexibility: Watch videos on any web-ready device.

Students Will Review:

This chapter helps students review the concepts in a triangles unit of a standard basic geometry course. Topics covered include:

  • Defining and classifying triangles
  • Triangle theorems and proofs
  • Identifying interior and exterior angles
  • Measuring angles
  • Defining the medians, altitudes and bisectors of triangles

9 Lessons in Chapter 5: Basic Geometry: Triangles
Triangles: Definition and Properties

1. Triangles: Definition and Properties

What makes a shape a triangle? In this lesson, we'll explore the definition of a triangle, then analyze the parts of triangles, including the vertices, base and height.

Classifying Triangles by Angles and Sides

2. Classifying Triangles by Angles and Sides

Not all triangles are the same. There are equilateral, isosceles and scalene triangles. Then there are right, acute and obtuse triangles. In this lesson, we'll learn how to classify triangles using their sides and angles.

Properties of Right Triangles: Theorems & Proofs

3. Properties of Right Triangles: Theorems & Proofs

In this lesson, you will learn about the properties of and theorems associated with right triangles, which have a wide range of applications in math and science. Specifically, we will discuss and prove the Pythagorean theorem and the right triangle altitude theorem. Let's get started.

Interior and Exterior Angles of Triangles: Definition & Examples

4. Interior and Exterior Angles of Triangles: Definition & Examples

Knowing just a few things about the interior or exterior angles of triangles is sometimes all you need to put all the pieces together. Find out more in this lesson.

Measuring the Angles of Triangles: 180 Degrees

5. Measuring the Angles of Triangles: 180 Degrees

Watch this video lesson to see why a triangle's angles always add up to 180 degrees. Also, learn how you can use this unique fact about triangles to find an unknown angle in a triangle.

Median, Altitude, and Angle Bisectors of a Triangle

6. Median, Altitude, and Angle Bisectors of a Triangle

Line segments in triangles are just clutter; they have special names and qualities depending on how they're drawn. In this lesson, we'll learn about medians, altitudes and angle bisectors.

Triangle Congruence Postulates: SAS, ASA & SSS

7. Triangle Congruence Postulates: SAS, ASA & SSS

When we have two triangles, how can we tell if they're congruent? They may look the same, but you can be certain by using one of several triangle congruence postulates, such as SSS, SAS or ASA.

The AAS (Angle-Angle-Side) Theorem: Proof and Examples

8. The AAS (Angle-Angle-Side) Theorem: Proof and Examples

When trying to find out if triangles are congruent, it's helpful to have as many tools as possible. In this lesson, we'll add to our congruence toolbox by learning about the AAS theorem, or angle-angle-side.

The Sierpinski Triangle & The Chaos Game

9. The Sierpinski Triangle & The Chaos Game

This lesson will give an explanation of what the Sierpinski Triangle is and two different ways it can be constructed. We will also look at the connection between the chaos game and the construction of the Sierpinski Triangle.

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