That would be a triangle.
Yes and it can have 3 or more straight sides
The description given fits that of a triangle.
No 3D shape with FLAT SIDES has exactly 3 faces. 4 is the minimum.
square
It's a polygon. three OR MORE sides.
Heptagon
Hexagon :)
a circle
A pentagon has five flat sides
The shape of 2D is a flat surface.
A rectangular shape has 6 flat sides. Those sides are the top, bottom, front, back, left and right,
No because it is flat 2d shape with 4 equal sides