Geometry

Types of Triangles

Lesson Contents

The 6 Main Types of Triangles: by Side and by Angle

Triangles types are named and classified by their sides and by their angles.

By Angle:
Acute Triangle — All angles are less than 90°.
Right Triangle — Has an angle that is exactly 90°.
Obtuse Triangle — Has one angle that is more than 90°.

By Side:
Equilateral Triangle — All three sides are equal in length.
Isosceles Triangle — Two sides are equal in length.
Scalene Triangle — Has no sides that are equal in length.

types of triangles

Special Types of Right Triangles

Within the right triangle, there are 4 special right triangles. The special right triangles by angles are the 45-45-90 Triangle and the 30-60-90 Triangle. The special right triangles by sides are the 3-4-5 Triangle and the 5-12-13 Triangle.

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