Types of Triangles
Types of Triangles
There are different types of triangles.
Triangles can be classified by:
Type of Triangle by Lengths of Sides
Triangles are a different type depending on how many sides are the same length (which is also how many angles are equal).
Equilateral triangles have 3 equal side lengths and angles.
3 sides are equal lengths.
Isosceles triangles have 2 equal side lengths and angles.
2 sides are equal lengths.
Scalene triangles have 0 equal side lengths and angles.
0 sides are equal lengths.
Type of Triangle by Angles
Triangles are a different type depending on the size of the angles inside the triangle.
Acute triangles have all acute angles (less than 90°).
3 angles are less than 90°.
Obtuse triangles have one angle that is obtuse (more than 90°, less than 180°).
1 angle is more than 90°.
1 angle is 90°.
More on Types of Triangles
Triangles can be classified by both lengths of sides and by angles. This means a triangle can be both acute and isosceles, or obtuse and scalene.
The slider below shows more real examples of the types of triangles:
What Is a Triangle?
A triangle is a 2-dimensional shape with three sides and three angles.
Indicating Equal Sides
If a triangle has sides of equal length, the equal sides are indicated by drawing a short line through the sides:
Indicating Equal Angles
Angles are indicated by drawing an arc between the sides.
Equal angles can be indicated by drawing the same number of arcs at each angle. The two angles with a two arcs are equal to each other:
The Interior Angles of a Triangle
The angles between the sides, that are inside the triangle, are called interior angles.
The interior angles of the triangle determine whether a triangle is acute, obtuse or right.
A triangle without a right angle is called an oblique triangle.
Acute triangles and obtuse triangles are both oblique triangles.