Search Triangle Educational Resources

Triangles are one of the basic shapes used in geometry and a fundamental concept in trigonometry. They are defined as polygons with three edges and three angles. Students as young as preschool can be introduced to triangles, but keeping track of the different types can be difficult. For more definitions and equations before starting on the resources, see the bottom of the page.

A triangle is a polygon that contains three edges and three angles, with the three angles always adding up to 180 degrees. Changing the lengths of the edges or the degrees of the angles can make a completely different triangle!

Types of triangles
There are three special types of triangles that are determined by looking at how many sides or angles are equal.

• Equilateral Triangle: This shape has three equal sides and three equal angles that are all 60 degrees
• Isosceles Triangle: For this triangle, only two of the sides are equal. Similarly, only two of the angles are equal (e.g. two angles are 40 degrees, while the third is 100 degrees).
• Scalene Triangle: This last triangle has no equal sides and no equal angles.

Types of angles
You can also the types of angles to identify a triangle:

• Acute Triangle: All three angles are less than 90 degrees (e.g. 70 + 60 + 50 = 180 degrees)
• Right Triangle: One of the angles is exactly 90 degrees (e.g. 90 + 60 + 30 = 180 degrees)
• Obtuse Triangle: One of the angles is greater than 90 degrees (e.g. 110 + 40 + 30 = 180 degrees)

Common Equations
Using some basic geometric formulas, you can easily calculate the area and perimeter of a triangle.

• Area: The area of a triangle can be found by taking half of the base and multiplying it by the height of the triangle (Area = ½ x base x height). If you need a refresher in multiplication, check out our multiplications page.
• Perimeter: The perimeter of the triangle is the distance around the edge of the triangle. In order to get the perimeter, you add up the lengths of all three sides.

Now that you have a basic understanding of triangles, check out the resources on this page or move over to the geometry page to see how other shapes are used in math.