Answer: True.
Explanation:
Since, A regular polygon is a polygon that is equi-angular (all angles are equal in measure) and equilateral (all sides have the same length).
Since, If a three sided polygon is a regular polygon.
⇒ The measurements of its all angles are same.
Therefore, measurement of its all angles is 60° ( because 180°/3)
⇒Also, It has the same edges.
Since, It is following the conditions of equilateral triangle.
Therefore, It must be an equilateral triangle.