A triangle (not traingle) is a polygon. It can be a regular polygon but need not be.
Eight sides
It is an equilateral polygon. It is not a regular polygon. For the polygon to be regular, it is not enough for the sides to be congruent: all the angles need to be congruent as well.
No. A polygon can be symmetric but need not be. In fact, the majority of polygons are not symmetrical.
It can be but need not be.
It can but need not.
No, a cylinder is not a polygon. It is not a polygon because it has curved sides. In order to be considered a polygon, it would need to have flat sides. Also, a polygon is a 2 dimensional shape but a cylinder is a three dimensional shape.
A polygon need not have any axes of symmetry. It can have at most n axes where n is the number of sides that the polygon has.
The parallel sides of a polygon are sides that are segments of parallel lines. A polygon need not have any parallel lines. A triangle, for example, is a polygon that cannot have parallel lines.
No. You also need all of the sides to be congruent. For example, a rectangle has four congruent angles, but it is not a regular polygon.
A regular polygon* * * * *It can be but need not be. A regular polygon must also have equal angles. A rhombus, for example, has equal sides, but is not regular. The correct term for the polygon is equilateral.
If every side of the polygon is the same length, then it is a regular polygon. If the measure of every internal angle of a polygon is the same as every other, then it is a regular polygon. The two always go together, so you need to check only one of the above criteria.