# Quadrilaterals

## Euclid (Book 1, Definition 22)

“Of quadrilateral figures, a square is that which is both equilateral and right-angled; an oblong that which is right-angled but not equilateral; a rhombus that which is equilateral but not right-angled; and a rhomboid that which has opposite sides and angles equal to one another but is neither equilateral nor right angled. And let quadrilaterals other than these be called trapezia.”

## Different Types of Quadrilaterals

RECTANGLE is a four-sided shape with four right angles, and includes:

SQUARE which has four right angles AND four equal sides

OBLONG which has four right angles BUT two pairs of equal sides (not four equal sides)

RHOMBUS is a four-sided shape with four equal sides BUT no right-angles

RHOMBOID is a four-sided shape with two pairs of equal sides, and opposite angles are equal (also a PARALLELOGRAM)

TRAPEZIUM is a four-sided shape with one pair of parallel sides (called a TRAPEZOID in America!)

TRAPEZOID is a four-sided shape with no parallel sides (called a TRAPEZIUM in America!)