# Types of Triangles # Types of Triangles

There are three basic types of triangles, and they are listed below in order of their base angles. Equilateral triangles have 60-degree base angles, meaning that the two base sides are congruent, and the angles on either side of the base angles are also congruent. Right triangles have 90-degree base angles, which means the two base sides are congruent, and the right angle at the base is congruent.

## 5 Types of Triangles You Need to Know

A triangle is simply a polygon with three straight sides. However, there are many types of triangles. So, here are 5 Types of Triangles You Need to Know.

#### 1. Equilateral

An equilateral triangle is a type of triangle with three sides equal in length. There are no obtuse angles. It’s most easily distinguished by the fact that its angles are 60 degrees each. The degree symbol ° is often appended to the outside corner angles to denote the difference between an equilateral and other types of triangles.

#### 2. Isosceles

An isosceles triangle has two sides of equal length and two angles that are also both the same. Two types of isosceles triangles exist, scalene (unequal) and equilateral (equal).

A scalene triangle has three unequal angles and a three-sided base. Equilateral triangles have angles of the same measures, and their base will have three equal sides.

#### 3. Right-angled

A right-angled triangle, the triangle where one angle is a right angle, has two equal sides and two equal angles. In a right-angled triangle, the hypotenuse is opposite the right angle (which, by definition, means that the other two sides are adjacent to it). The legs or base of the right-angled triangle can be calculated as length ‘a’. One leg can be calculated as 2 * length ‘a’.

An acute triangle is any triangle with angles less than 90 degrees. Two angles add up to 180 degrees, and one side must be obtuse for an acute angle in a triangle.

#### 4. Scalene

A scalene triangle is an irregular polygon in which all sides are different. It has no side that is the same length as any other, so it cannot be inscribed in a circle. Scalene shapes have three points, one more than a kite or equilateral triangle. The more sides the scalene polygon has, the less symmetrical it will be. Scalene shapes have three points because their measurements require three different units: feet, meters, and inches are good units for this purpose.

Types of Scalene Triangles

A scalene triangle can also be classified according to its measure (i.e., obtuse scalene). An obtuse scalene triangle contains two acute angles, two right angles, and two obtuse angles.

#### 5. Acute triangle

An acute triangle is a triangle with all three angles less than 90 degrees. The lengths of its three sides determine the sizes and shapes. Acute triangles are also classified into two categories: scalene and isosceles. Scalene or unequal, acute triangles have two sides that are unequal in length, while isosceles, or equal, have two sides that are equal in length. A right-angled triangle has only one angle that is 90 degrees—thus, it has a total angle sum of 180 degrees. 