A triangle is a three-sided polygon, in which we use straight segments for the sides. It is a particular case of quadrilaterals, as it is a quadrilateral divided by 2. Definition: Given three non-collinear points A, B and C1, the meeting of the segments $\overline{AB}$, $\overline{AC}$ and $\overline{BC}$ is called a triangle. Basic elements Vertices: can be defined as meeting points between the sides of a triangle. Generally speaking, vertices are meeting points between sides of any polygon. From the previous figure, points A, B and C are vertices of the triangle ($\Delta ABC$) In particular, a triangle is formed by 3 vertices.