A regular polygon like an equilateral triangle.
Only when it is a regular polygon that all interior angles are of equal measure
a "regular" polygon
Only if the polygon is "regular".
All of the angles are equal in a "regular" polygon. (All of the sides are too.)
Only if the polygon is a "regular" one.
They may, or may not, be equal. If you are talking about a regular polygon, all angles are equal in measure. If it is not a regular polygon, the angles are most likely different.
It is then called a regular polygon when all angles and sides are of equal values.
This is a tautological question that does not have a proper answer. A regular polygon is one which has all its sides of equal length and all its interior angles of equal measure.
A rhombus has four sides of equal lengths. So it is an equilateral polygon. But it is not an equiangular. It's angles are not equal in measure.
pentagon
An equilateral triangle.
regular