How to Identify Different Types of Triangles

By Ainsley Patterson

Geometry can be one of the most confusing years of math in high school. With all the different shapes, types of angles, and formulas to remember, you may start to feel that you are swimming in a sea of confusion. Let me ease your confusion by guiding you through how to identify different types of triangles.

Take a moment to look at the sides and angles of the triangle. Measure all three sides with a ruler and all three angles with a protractor. Make sure that you write down their measurements as you take them.

Look at the measurements of the sides that you have written down and ask yourself if they are all the same. If all three sides of a triangle are the same length then the triangle is an equilateral triangle.

Ask yourself if two sides of your triangle are the same length. If your triangle has two sides of the same length then this triangle is an isosceles triangle.

Label your triangle as a scalene triangle if all the sides of your triangle have a different length.

Look at the angle measurements of your triangle and ask yourself if all the angles have a measurement of less than 90 degrees. An angle that is less than 90 degrees is called an acute angle, therefore a triangle whose angles are all less than 90 degrees in measure is called an acute triangle. If your triangle is an acute triangle where all of the angles have the same measurement then you can further label your triangle as an equiangular triangle. Since the sum of all the angles of a triangle is 180 degrees, another way to identify an equiangular triangle is to see that all of the triangle's angles measure 60 degrees.

Ask yourself if your triangle has an angle that measures greater than 90 degrees. An angle whose measure is greater than 90 degrees is an obtuse angle, therefore a triangle with an angle that measures greater than 90 degrees is an obtuse triangle.

Check if your triangle has an angle whose measure is 90 degrees. A 90-degree angle is a right angle, so a triangle with an angle that measures 90 degrees is a right triangle. In a right triangle the two angles whose measure are not 90 degrees are complementary angles, because added together they equal 90 degrees (since the sum of the angles in a triangle is 180 degrees). Also, in a right triangle, the side opposite the 90-degree angle is known as the hypotenuse.

About the Author

Based in Ypsilanti, Mich., Ainsley Patterson has been a freelance writer since 2007. Her articles appear on various websites. She especially enjoys utilizing her more than 10 years of craft and sewing experience to write tutorials. Patterson is working on her bachelor's degree in liberal arts at the University of Michigan.