Question

An equilateral triangle is an example of what kind of polygon? Convex, concave or irregular?

Answer 1

Equilateral triangle is a regular three-sided polygon.
It has three interior angles of `60^o` each and three sides, equal in length.
It's an example of a convex polygon.

Explanation:

There are a few different but equivalent definitions of a convex polygon.

One of them is as follows.
A polygon is called convex if all its interior angles are less than `180^o`. Equilateral triangle is, obviously, of this kind.

Another definition is as follows.
A polygon is called convex if a segment that connects any two of its vertices lies within the boundaries of a polygon. Equilateral triangle, obviously, satisfies this definition.