Triangles are classified into different types based on their angles and the lengths of their sides. Relations between angles and side lengths are a major focus of trigonometry. In particular, the sine, cosine, and tangent functions relate side lengths and angles in right triangles.
Triangles are classified into two groups: based on sides, 1) scalene, 2) isosceles, and 3) equilateral triangles; based on angles, 1) acute angle, 2) obtuse angle, and 3) right or right-angled triangles.
The following figures show the different types of triangles. Scroll down the page if you need more explanations and examples of each type of triangle and how to solve problems involving them.