Answer
a) An equilateral triangle exists, but a concave triangle does not.
b) A equilateral pentagon and a concave pentagon both exist.
Work Step by Step
An equilateral polygon has the same angle and side length everywhere. Thus, both a triangle and a pentagon can be equilateral. A concave polygon has one angle which is between 180 and 360 degrees. This is possible for a pentagon but not for a triangle.
