Types of Triangles

Triangles can be classified by various properties relating to their angles and sides. The most common classifications are described on this page.

---

Classifications of Triangles

Right Triangles
 

A right triangle has one 90° and a variety of often-studied properties including: Right Triangle Calculator Proof of Pythagorean Theorem Pythagorean Triplets Sine, Cosine, Tangent Pictures of Right Triangles 7 24 25 Right Triangle Images 3 4 5 Right Triangles 5 12 13 Right Triangles

The Equilateral triangle shown on the left has three equal sides and three equal angles.
Each angle is 60°

The Isosceles triangle shown on the left has two equal sides and two equal angles.

The Scalene Triangle has no congruent sides. In other words, each side must have a different length..

The Acute Triangle has three acute angles (an acute angle measures less than 90°)

The  Obtuse Triangle has an obtuse angle (an obtuse angle has more than 90°). In the picture on the left, the shaded angle is the obtuse angle that distinguishes this triangle

Since the total degrees in any triangle is 180°, an obtuse triangle can only have one angle that measures more than 90°.