decagon
A regular decagon would have five sets or parallel lines.
2 lines of symmetry
10
There are infinitely many lines of symmetry. Every line can be a line of symmetry for a suitable shape.
A decagon need not have any lines of symmetry. It can also have 1 or 10 lines of symmetry.
A decagon need not have any lines of symmetry. It can have 10.
A dodecagon need not have any lines of symmetry. It can have a maximum of 12.
10
Ten.
7
6
decagon
None are guaranteed.If it is a regular decagon (convex, with all side lengths equal and all angle measures equal), then there are 10 lines of symmetry.
A decagon and any polygon above a pentagon has more than two lines of symmetry
A regular decagon has rotational symmetry = 10.For irregular decagons, it could be less (either 2 or none.)
There need not be any.