you can find a line of symmetry when the shape can be folded and not cross over
You can find many lines of symmetry in nature.
i section
radial symmetry, i am trying to find the reason now!
You can find more about symmetry from Khan Academy, or just by simply searching "symmetry" in a basic Mathematics textbook. Usually, good results can be found on Wikipedia.
A square has 4 lines of symmetry.
You can find lines of symmetry without tracing but tracing helps you get a better picture of it.
in a book
It would be hard to find a line of symmetry on a moon, as it is likely to be irregularly shaped.
X= -b / 2a
An equilateral triangle has 3 lines of symmetry which perpendicularly bisects each of its vertices
There are an infinite number of lines of symmetry in a circle, as any diameter will be a line of symmetry and there are an infinite number of angle measure for that line to pass through.
You can flip the traced version along various lines. If the flipped shape matches the original then the that is a line of symmetry. Alternatively, if you can find a fold such that the two halves of the tracing match then the fold line is a line of symmetry.