Here mine dog "Flame" has her confront made perfectly symmetrical through a bitof picture magic.

The white line down the center is theline of Symmetry


When the folded component sits perfect on top (all edges matching), then the fold line is a heat of Symmetry.


Here I have actually folded a rectangle one way, and it didn"t work.

*
So this is not a line of Symmetry

But as soon as I shot it this way, that does work (the folded component sits perfect on top, every edges matching):

*
So this is a line of Symmetry

Triangles

A Triangle can have 3, or 1 or no lines of symmetry:

*
*
Equilateral Triangle(all political parties equal, all angle equal) Isosceles Triangle(two political parties equal, 2 angles equal) Scalene Triangle(no sides equal, no angles equal)
3 currently of Symmetry1 heat of SymmetryNo lines of Symmetry

Quadrilaterals

Different varieties of square (a 4-sided airplane shape):

*
*
Square(all political parties equal, all angles 90°) Rectangle(opposite sides equal, all angle 90°)Irregular Quadrilateral
4 currently of Symmetry2 lines of SymmetryNo present of Symmetry

*
*
KiteRhombus(all sides equal length)
1 line of Symmetry2 currently of Symmetry

Regular Polygons

A consistent polygon has actually all political parties equal, and also all angle equal:

An Equilateral Triangle (3 sides) has 3 present of Symmetry
A Square (4 sides) has 4 lines of Symmetry
*
A Regular Pentagon (5 sides) has 5 lines of Symmetry
*
A Regular Hexagon (6 sides) has 6 present of Symmetry
*
A Regular Heptagon (7 sides) has 7 present of Symmetry
*
A Regular Octagon (8 sides) has 8 lines of Symmetry

And the sample continues:

A regular polygon the 9 sides has 9 lines of SymmetryA constant polygon the 10 sides has 10 currently of Symmetry...A continuous polygon that "n" sides has "n" currently of Symmetry

Circle