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Math for Kids23 chapters | 325 lessons

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Lesson Transcript

Triangles may be a simple shape but there are lots of different types! In this lesson, we will clearly define a triangle and think about some of the different kinds of triangles.

Triangles are very common shapes. We see them on road signs, on houses, and in food (think chips or pizza). When you think of a triangle, you might imagine three equal sides because we see this type of triangle a lot in our daily lives, but did you know that there are lots of different types of triangles? Triangles can be stretched out and tall like the Eiffel Tower or short and squished like a hanger. What are some other examples of different types of triangles that you can think of?

All types of triangles can be grouped or categorized. Triangles are categorized by the length of their sides and the size of their angles. Before we get into the different types of triangles, take a minute and think about what a triangle is. (Hint: 'tri' means three)

Simply put a **triangle** is a shape with three sides and three angles. With a definition that simple, there are bound to be lots of different kinds. As we explore all the different types of triangles, remember the three must-haves for a shape to be a triangle. The shape must have:

- 3 sides
- 3 angles
- All of the angles add up to 180 degrees

Like we talked about before, triangles are categorized by the length of their sides and the size of their angles. First let's look at the three different categories of triangles based on the length of their sides.

**Equilateral**: All sides are equal. All angles are equal.**Isosceles**: Two sides are equal. Two angles are equal.**Scalene**: No sides are equal. No angles are equal.

Now let's move on to the angles. An **angle** is the space between two lines that connect and form a point. In this case, angles are where the sides of the triangles meet. Angles are measured in degrees. These degrees are not like temperature, they measure how big or small an angle is, not how hot or cold it is outside.

If an angle is less than 90 degrees, it is an acute angle. If an angle is bigger than 90 degrees, it is an obtuse angle. Think of 90 degrees as the sweet spot.

**Acute**: All angles are less than 90 degrees.**Obtuse**: One angle is greater than 90 degrees.**Right**: One angle equals 90 degrees.

Remember, a triangle is categorized by its sides and its angles so a triangle can be both an equilateral and acute or scalene and obtuse.

Let's review. **Triangles** have three sides and three angles. All three angles must add up to 180 degrees. Triangles can be categorized by their sides (**equilateral, isosceles**, or **scalene**) and by their angles (**acute, right**, or **obtuse**). Triangles have a simple definition but there are lots of different kinds for you to build and explore!

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Additional Activities

There are triangles everywhere in the real world. In this activity, we will hunt for triangles in real life and classify the triangles based on their side lengths (and angle measurements, too, for an extra challenge!)

- Paper and pencil for writing down the triangle measurements and classification
- Ruler or measuring tape
- Protractor (if you wish to take on the added challenge of classifying based on angle measurements)

1) Look around for a triangle to measure. You can look inside or outside (with permission of course!) Some places you may find triangles are: different foods, street signs, hangers, parts of buildings, and more.

2) When you find a triangle, write down a description of the triangle (what the object is, where you found it, ...)

3) Take your ruler or measuring tape and measure all three sides of the triangle. Write down the three measurements.

4) Classify the triangle by its side measurements. Is it equilateral (all sides equal)? Isosceles (2 sides equal)? Scalene (no sides equal)?

5) Optional - Use a protractor to measure the three angles of the triangle. Write down the three measurements.

6) Optional - Classify the triangle by its angle measurements. Is it acute (all angles smaller than 90°)? Obtuse (one angle larger than 90°)? Right (one angle equal to 90°)?

7) Repeat until you have found and classified many triangles.

Through this triangle hunt, you will gain measurement skills and understand how to classify triangles. You may be surprised how many triangles are out there!

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Math for Kids23 chapters | 325 lessons

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