Sides of a Triangle

Three Line Segments
Three Line Segments

The three line segments which form a triangle are defined sides of the triangle.

Three line segments are essential to form a triangle, which is constructed such that connecting endpoints of them to form a closed geometrical shape. Each line segment of the triangle is now called as a side of the triangle. Total three line segments are used to construct a triangle and they are known as sides of the triangle.


Geometrically, line segments are known as line segments when they are in free stage on a plane. If in case they are connected each other to form a triangle, all three line segments become sides of the triangle.

Three Line Segments become sides of triangle
Sides of a Triangle

Sides of the triangle usually do not have special names in almost all types of triangles but except in the case of one triangle and it is right angled triangle. Right angled triangle is a very special one and all three sides are having three different names.

  1. Opposite Side
  2. Adjacent Side
  3. Hypotenuse
Sides of a right angled triangle
Sides of a Right Angled Triangle


Sides of any type of triangle are line segments. So, the system of representing a line segment is used as system of representing every side of the triangle to express sides of the triangle in mathematical form.

The triangle ABC is formed by three line segments. Sides of ΔABC are written as AB, BC and CA in mathematics but length of three sides are simply written as AB, BC and CA respectively.

In the same way, sides of the ΔXYZ are written as XY, YZ and ZX in mathematics and their lengths are expressed in mathematics as XY, YZ and ZX respectively.

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