perimeter
The distance around a closed plane figure is called the perimeter. The perimeter of a figure can be calculated by adding together the lengths of each side.
A circle.
A circle.
plane figure
Perimeter
It is a polygon that is a closed plane figure with 3 or more straight lines.
A three sided closed plane figure (shape) is a triangle.
No. A plane extends to the ends of the universe.
a closed plane figure with 3 or more line segments is a polygon
is a closed plane figure
Circle
If they are straight sides, then a polygon. Otherwise, simply "a closed plane figure with 3 or more sides".