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).

Triangles are equilateral, isosceles or scalene depending on whether 3, 2 or 0 side lengths and angles are equal.

Equilateral Triangles

Equilateral triangles have 3 equal side lengths and angles.

3 sides are equal lengths.

3 angles are equal (60°).

Isosceles Triangles

Isosceles triangles have 2 equal side lengths and angles.

2 sides are equal lengths.

2 angles are equal.

Scalene Triangles

Scalene triangles have 0 equal side lengths and angles.

0 sides are equal lengths.

0 angles are equal.

Type of Triangle by Angles

Triangles are a different type depending on the size of the angles inside the triangle.

Triangles are acute, obtuse or right triangles depending on whether all angles are acute (less than 90°), one angle is obtuse (more than 90°) or one angle is a right angle (90°).

Acute Triangles

Acute triangles have all acute angles (less than 90°).

3 angles are less than 90°.

Obtuse Triangles

Obtuse triangles have one angle that is obtuse (more than 90°, less than 180°).

1 angle is more than 90°.

2 angles are less than 90°.

Right triangles have one right angle (90°).

1 angle is 90°.

2 angles are less than 90°.

Slider

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.

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See Also

What is a triangle? What is an angle? What is an acute angle? What is an obtuse angle? What is a right angle? What are the interior angles of a triangle? Learn more about the types of triangles ( interactive widget)