What is a Triangle?
Basics on the topic What is a Triangle?
Triangles
Do you know what a slice of watermelon and a slice of pizza have in common?
They both have the shape of a triangle! What exactly does this mean? If you want to find out more about triangles, continue reading.
What Are the Attributes of a Triangle?
An attribute of a triangle is something the shape must have to be called a triangle. It must be a closed shape that has 3 sides, 3 corners and 3 angles.
Attributes can be put into two categories: defining attributes and nondefining attributes.
Defining Attributes of a Triangle
What are the 3 defining attributes of a triangle?
A triangle has 3 sides:
A triangle has 3 corners:
A triangle has 3 angles:
NonDefining Attributes of a Triangle
A triangle can be any size:
A triangle can be any color:
A triangle can face in any direction:
Triangles – Summary
You can find the defining and nondefining attributes of triangles listed in the table below.
Defining attributes of triangles  Nondefining attributes of triangles 

three sides  size 
three corners  color 
three angles  direction 
Following the video, you will find attributes of a triangle worksheets suitable for first grade.
Transcript What is a Triangle?
Nico and Nia are having lunch at their favorite restaurant,(...)Three Corners Cafe. “I sure am hungry, Nia!” “MEEEE TOOOO!” “Everything looks delicious!” “How are we going to choose what to eat?” " We can order the Three Corners Special." "What is the Three Corners Special?" " It is any food on the menu that is a triangle shape!" : "But how will we know which food is a triangle?" We can help Nico and Nia order their lunch by finding foods that are in the shape of Triangles A triangle is a shape. Shapes are twodimensional figures that we can name based on their "defining attributes". Defining attributes are characteristics that a shape MUST HAVE. Let's look at a triangle. The defining attributes of a triangle are that it must be a closed shape that has… three sides… three corners… and three angles… Shapes also have NONdefining attributes. If defining attributes are characteristics a shape MUST have, what are nondefining attributes? A NONdefining attribute is something that a shape has, but doesn’t always have to be the same. SIZE is an example of a nondefining attribute. A triangle can be big(...), big,(...) BIG… or a triangle can be small,(...)small,(...)_ small. Color is another nondefining attribute. Triangles can be ANY color! Triangles can also face many different directions. Let's identify some triangles! Is this a triangle? Start by counting the sides… It has one,(...) two, (...) three sides. Now count the corners. It has one,(...), two,(...) three corners. Finally, count the angles on the inside. It has one, (...) two,(...) three angles on the inside. Yes, this shape is a triangle! How about this shape? Is this shape a triangle? Start by counting the sides. One,(...) two, (...), three, (...) FOUR. Wait a minute (...) this shape has FOUR sides! Since we know that triangles MUST have three sides, we know that this is NOT a triangle! Let’s try ONE more! Count the sides… Count the corners... Count the angles. Yes, this is a triangle because it has all the defining attributes of a triangle. Now that we know all the attributes of a triangle, let’s help Nico and Nia find which foods to order for lunch. Look at the menu! Can you point to all of the foods that have a triangle shape? Here’s one! (...) This slice of pizza! This slice of pizza has all the attributes of a triangle! Here is another one! A triangle is made by this half of a sandwich! There is one on this slice of cake! And the last one is found from this slice of watermelon! Remember, (...) Shapes have defining and nondefining attributes A triangle is a closed shape that always has three sides, three corners, and three angles. But, a triangle can be any size(...) or color(...) and face any direction. "Yum! This lunch is delicious!" "Yes! It's TRIiffic!"
What is a Triangle? exercise

Help Nico to remember what he learned about triangles.
HintsThis is an example of a triangle.
Count the sides, corners, and angles of this triangle.
SolutionDefining attributes are characteristics that a shape must have.
A triangle has 3 sides.
A triangle has 3 corners.
A triangle has 3 angles. 
Identify the triangles in Nico's artwork!
HintsTriangles have 3 sides, 3 corners, and 3 angles.
Triangles can be different sizes, colors, and directions.
There are 5 triangles in the picture.
SolutionThere are 5 hidden triangles in Nico's artwork.
Triangles have: 3 sides
 3 corners
 3 angles
 sizes
 colors
 directions

How many triangles do you see?
HintsA triangle has 3 sides, 3 corners, and 3 angles.
These are examples of triangles.
Triangles can be different colors, shapes, and directions.SolutionThere are 3 triangles in the picture.
These shapes have: 3 sides
 3 corners
 3 angles

How many triangles do you see in each picture?
HintsTriangles have 3 sides, 3 corners, and 3 angles.
These are examples of triangles.
SolutionA triangle is a closed shape with 3 sides, 3 corners, and 3 angles.
The house has 1 triangle.
The kite has 4 triangles.
The sailboat has 2 triangles.
The desert has 3 triangles. 
Which shape is a triangle?
HintsA triangle is not round.
A triangle does not have 4 sides.
SolutionThis is a triangle.
A triangle has: 3 sides
 3 corners
 3 angles

Which shape am I?
HintsDefining attributes are characteristics that a shape must have.
Counting the number of sides, corners, and angles can help you to figure out the shape.
SolutionA square has:
 4 sides
 4 corners
 4 angles
 sides that are all the same length
A triangle has:
 3 sides
 3 corners
 3 angles
A circle is round. It has:
 no sides
 no corners
 no angles
A rectangle has:
 4 sides
 4 corners
 4 angles