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!)

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