An equilateral triangle.
octagon
a square
A square
It depends on the shape, whether or not it is regular, etc.
A heptagon.
An octagon.
A triangle as no other 2d shape can have 3 sides.
It is a rhombus or a parallelogram.
a irregular polygon and rhombus
A 2D square □
a shape that's sides a not the same length and angles are not the same degree