Triangle

Triangle is made by joining any 3 non-collinear points.

It is a 3 sided polygon.

Polygon

Polygon is a simple closed figure made of line segments

A triangle has

  3 vertices − A, B, C

  3 sides −     AB, BC, AC

  3 angles − ∠A, ∠B, ∠C

Interior and Exterior of a Triangle

Here,

• P, Q are in interior of ∆ABC
• R is on triangle ∆ABC
• X, Y are in exterior of ∆ABC