Of trilateral figures, an equilateral triangle is that which has its three sides equal, an isosceles triangle that which has two of its sides alone equal, and a scalene triangle that which has its three sides unequal.
“Isosceles Follies” is composed solely of the two isosceles triangles shown below.
Of trilateral figures, an equilateral triangle is that which has its three sides equal, an isosceles triangle that which has two of its sides alone equal, and a scalene triangle that which has its three sides unequal.
“Isosceles Follies” is composed solely of the two isosceles triangles shown below.
Euclid’s Elements – Book 1 – Definitions, definition XXII, simply says:
“A quadrilateral figure is one which is bounded by four sides.”
So any four sided shape is a quadrilateral. The shape I use in this piece is a form of a quadrilateral that Euclid describes as a kite. Yes, it’s the shape your thinking of, like the traditional flying kite shape.
Per Wikipedia: In Euclidean geometry, a kite is a quadrilateral whose four sides can be grouped into two pairs of equal-length sides that are adjacent to each other. In contrast, a parallelogram also has two pairs of equal-length sides, but they are opposite to each other rather than adjacent.
The diagonals of a kite are always perpendicular to each other.