How do you go about identifying shapes? If you're like most kids learning the basics of geometry, you probably begin by counting the number of sides. For example, if you see a shape with four sides, what would it be? Depending upon the lengths of the sides, you've got either a square or a rectangle.
If you run across a shape with three sides, what do you call it? If you said triangle, you got it! But what kind of triangle is it? Did you know that there's more than one type of triangle? It's true! Thanks to the great minds of geometry over the ages, the simple three-sided triangle has been further defined in a variety of ways.
In addition to three sides, every triangle also has three angles. Those three angles always add up to 180º. Mathematicians have given triangles special names based upon how many of those angles are equal.
An isosceles triangle has two equal angles (and two equal sides). The angles can vary, as long as two are equal. For example, a triangle with two 70º angles and one 40º angle would be an isosceles triangle.
If you've been counting carefully, you know there's one more option. If a triangle doesn't have two or three equal angles, it could have zero equal angles. These triangles, which also don't have any equal sides, are known as scalene triangles.
Can you believe that there are three different types of triangles? But wait…there's more! Geometry experts weren't satisfied with just three types of triangles. They also decided to classify triangles based upon the type of angles inside the triangle.
For example, a triangle with a right angle, which is an angle equal to 90º, is known as a right triangle. Some triangles, however, have three angles that are all less than 90º. Such a triangle is called an acute triangle. A triangle can also have an angle more than 90º. Those triangles are called obtuse triangles.
Of course, there can be even more varieties of triangles, because you can combine the names based upon their features. For example, if you have a triangle with angles of 45º, 45º, and 90º, it would be a right isosceles triangle. It's a right triangle, because it has a 90º angle. It's an isosceles triangle because it has two equal angles of 45º.