Kesavan from Latymer All Saints C of E Primary sent the following designs, which all have a vertical line of symmetry:
I know that my triangle is symmetrical because when you fold it in half vertically, both sides are exactly the same. Another way of showing this is putting a mirror on the line of symmetry. If you look at it from one side, it will look the same as the normal triangle.
Rayyan from Doha College in Qatar sent in the following:
Shawn from Lanesborough School in Surrey sent in a picture.
Well done for producing these triangles with symmetry, perhaps there are more that others could find.