Theory:

It is a \(3\) sided polygon. It is also the polygon with the least number of the sides.
u.PNG
 
Vertices: \(A\), \(B\) and \(C\) are common endpoint in triangle.
 
Sides: \(AB\), \(BC\) and \(CA\) are the ray forming the angles in triangle.
 
Angles: \(∠A\), \(∠B\) and \(∠C\) are a two ray which share a common endpoint.
 
A triangle is also associated with \(3\) parts:
  • Interior of triangle is refers to the inside/inner area.
  • Boundary of triangle is refers to the dividing line thus it divides the interior and exterior of the triangle
  • Exteriorof triangle is refers to the outside / outer area.
Video: parts of a triangle