A 2D shape is symmetrical if you can draw a line through it and it looks exactly the same either side. This line is called a line of symmetry. Oh that rather smug expression tells me that square ...

However, I can offer a relatively simple way to draw such a shape using a straight edge and compass. Take an equilateral triangle and extend its sides out across the page. Now, draw an arc centred ...

A 2D shape is symmetrical if a line can be drawn through it so that either side of the line looks exactly the same. The line is called a line of symmetry. This is sometimes called a 'mirror line ...