### Right Triangle

#### Lesson Objective

In this lesson, we will learn about right triangles (also called right-angled triangle)...

#### About This Lesson

In this lesson, we will:

- learn what are right triangles.
- see some examples on identifying them.

The study tips and math video below will explain more.

### Study Tips

#### Tip #1

When one of the internal angle of a triangle is equals to 90°, this triangle can be called a right triangle. See the examples below:

#### Tip #2

A right triangle can also be an isosceles triangle if the two sides that form the 90° angle are equal in length. See the picture below:

### Math Video

#### Lesson Video

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#### Math Video Transcript

00:00:03.190

In this lesson, we will learn about right-angled triangle (RT).

00:00:08.050

For a triangle, to be called a RT, one of its internal angles must be 90 degrees.

00:00:15.220

Now, let's move vertex 'A', and see what happens.

00:00:21.010

Notice that, when the angle at vertex 'B' becomes 90 degrees, this triangle becomes a RT.

00:00:29.210

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

00:00:34.140

Here, we get another RT, when the angle at vertex 'A' is 90 degrees. Let's continue.

00:00:45.240

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

00:00:54.000

As we move vertex 'A' further to the right, the angle at vertex 'C' becomes 90 degrees.

00:01:01.140

Therefore, we have another RT.

00:01:06.120

Now, observe the different sizes of a RT, when we move the vertex 'A' and 'C' together.

00:01:22.210

Let's see some examples.

00:01:26.080

Is this a RT?

00:01:29.150

Notice that, one of the internal angles is 90 degrees.

00:01:34.070

Therefore, this is a RT.

00:01:39.030

Next example, how about this triangle?

00:01:45.100

Now, none of these angles are 90 degrees.

00:01:49.200

Hence, this is not a RT.

00:01:54.130

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 right triangle or pick your choice of question below.

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