Theory:

A three sided polygon is called a triangle. It contains three vertices, three sides and three angles. Triangle is the polygon with the least number of sides.
 
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Vertices: \(A\), \(B\) and \(C\)
 
Sides: \(\overline {AB}\), \(\overline {BC}\) and \(\overline {CA}\)
 
Angles: \(\angle A\), \(\angle B\) and \(\angle C\)
 
A triangle is also associated with \(3\) parts:
  • The interior of a triangle refers to the inside/inner area of a triangle.
  • The boundary of a triangle refers to the line which divides the interior and exterior part.
  • The exterior of a triangle refers to the outside / outer area of a triangle.
Parts of a triangle: