Triangle is the simplest polygon of all the closed figures formed in a plane by three line segments. It is a closed figure formed by three line segments having six elements - three angles (i) ∠ABC or ∠B (ii) ∠ACB or ∠C (iii) ∠CAB or ∠A and three sides - (iv) AB (v) BC (vi) CA.
It is named as Δ ABC or Δ BAC or Δ CBA and read as triangle ABC or triangle BAC or triangle CBA.
Triangles can be classified into different types in two ways:
On the basis of sides
On the basis of angles