Types of Triangles

Lesson Plan - Get It!

Audio:

Read the section below to learn about the different types of triangles.

A triangle has three sides and three angles. A triangle is also a two-dimensional shape; that means it is a flat shape.

1. Look at the triangles below. What do you notice about each triangle?
2. Label a sheet of lined paper with the numbers "1-6." Make sure you leave enough space between each number to draw a triangle.
3. Draw each triangle below.
4. When you are finished drawing each triangle, write a sentence about each one describing what the triangle looks like:

• What did you write about each triangle?
• Did you talk about the sides or angles?
• Did you talk about the size of the triangles?

Let's start learning about the different types of triangles.

The first triangle you will learn about today is the equilateral triangle. An equilateral triangle has three sides that are the same length and three angles that are the same. All of the sides are congruent, and all of the angles are congruent. Congruent means that they are the same or equal. One way to remember an equilateral triangle is by remembering that all sides are equal and you can hear the word "equal" in equilateral.

The second triangle you will learn about is called a right triangle. A right triangle has one ninety-degree angle. The right triangle below has a little box in the corner. This box tells us where the right angle is. One way to remember a right triangle is by looking at the shape of the triangle. It looks similar to a ramp you would use for a car. Look at the right triangle below. What do you notice about it?

The next triangle is called an isosceles triangle. An isosceles triangle has two sides that are the same length and two angles that are the same size. In other words, an isosceles triangle has two congruent sides and two congruent angles. Look at the triangle below. Can you identify the sides that are the same length?

An obtuse triangle has one angle that is bigger than ninety degrees (this means its angle is bigger than the one found on a right triangle). An angle that is greater than ninety degree is called an obtuse angle. Can you identify the angle on the obtuse triangle that is bigger than ninety degrees? Tell an adult which angle is bigger than ninety degrees. Great!

The next triangle you will learn about today is called an acute triangle. All the angles on an acute triangle are less than ninety degrees. Angles that are less than ninety degrees are called acute angles. A good way to remember an acute triangle is to remember its angles are small (less than 90 degrees) and cute (acute).

The last triangle you will learn about is called a scalene triangle. A scalene triangle has three unequal sides. Each side has a different length than the others an a scalene triangle.

Now that you know how to tell the differences among the different types of triangles, you are ready for some extra practice. Move on to the next section in the lesson to learn more about the different types of triangles.