How many lines of symmetry does LINES have?

Answer 1

If the question refers to a single completely geometrically straight line of finite length in a plane, then a straight line will have two lines of symmetry. One symmetry line is perpendicular to the line being discussed and one symmetry line coincides with the line being discussed.

The symmetry operation here is the one where every point of the figure is flipped perpendicularly across the symmetry line and the object is symmetric if that flipping produced exactly the same set of points. (Said differently, if flipping the set of points through a line produced an exact replica of the original set of points, then the like determining the flip is a symmetry line.)

One level of complication occurs if the straight line which is the subject of the symmetry question is an infinitely long straight line. In such a case one symmetry line still coincides with the actual line, but all lines that are perpendicular to the straight line will be lines of symmetry. Thus, an infinitely long straight line has no single point as its "middle" and has an infinitely many symmetry lines consisting of all possible lines perpendicular to the original line.