Types of Triangles

A right triangle has one 90° angle and a variety of often-studied topics:

• 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
• Right Triangle Calculator

The Equilateral triangleshown on the left has three congruent sides and three congruent 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°.