### Obtuse Triangle

#### Lesson Objective

In this lesson, we will learn about obtuse triangles...

#### About This Lesson

In this lesson, we will:

- learn what are obtuse triangles.
- See some examples on identifying them.

The study tips below will give you a short summary on this.

The math video below will explain in depth about this. Furthermore, it will show some examples so that you can understand this lesson better.

### Study Tips

#### Tip #1

When one of the internal angle of a triangle is greater than 90Â°, this triangle can be called an obtuse triangle. See some examples below:

The math video below will explain more...

### Math Video

#### Lesson Video

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#### Math Video Transcript

00:00:03.120

In this lesson, we will learn about obt. triangles (OT).

00:00:08.070

A triangle is an OT, when it has an internal angle that is greater than 90 degrees.

00:00:17.120

Now, to demonstrate this, let's move vertex 'A' to the left

00:00:26.050

Notice that, when the angle at vertex 'B' is greater than 90 degrees, this triangle becomes an OT.

00:00:34.230

Next, let's move this vertex, to the right..

00:00:40.100

Here, we get another OT, when the angle at vertex 'C', is greater than 90 degrees.

00:00:48.120

Let's move vertex 'A'…and vertex 'C'.

00:00:55.220

Again, we get another OT, when the angle at vertex 'A' is greater than 90 degrees.

00:01:04.120

Let's see some examples.

00:01:07.120

Is this an OT?

00:01:12.070

Notice that, this angle is greater than 90 degrees.

00:01:17.010

Therefore, this is an OT.

00:01:21.090

Next example, how about this triangle?

00:01:28.180

In this triangle, there are no angles that are greater than 90 degrees.

00:01:34.100

Hence, this is not an OT.

00:01:38.140

That is all for this lesson.

### Practice Questions & More

#### Multiple Choice Questions (MCQ)

Now, let's try some MCQ questions to understand this lesson better.

You can start by going through the series of questions on obtuse trianglesor pick your choice of question below.

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