Here my dog "Flame" has actually her face made perfect symmetrical through a bitof picture magic.

The white line under the center is present of Symmetry


When the folded part sits perfectly on peak (all edges matching), climate the fold line is a line of Symmetry.


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

*
So this is not a line of Symmetry

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

*
So this is a heat of Symmetry

Triangles

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

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

Quadrilaterals

Different species of square (a 4-sided plane shape):

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

*
*
KiteRhombus(all sides equal length)
1 heat of Symmetry2 present of Symmetry

Regular Polygons

A continual polygon has actually all sides equal, and also all angles equal:

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

And the sample continues:

A consistent polygon that 9 sides has 9 lines of SymmetryA constant polygon that 10 sides has actually 10 lines of Symmetry...A continual polygon the "n" sides has actually "n" present of Symmetry

Circle