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1.1.4.QUADRILATERALS
Apolygonwithfoursidesiscalledquadrilateral.
Aparallelogramisaquadrilateralwithtwopairsofparallelsides(Figure1.13).
Diagonalsofaparallelogrambisecteachother.
Figure1.13.Parallelograms
Arectangleisaparallelogramwhoseanglesareright.Diagonalsofarectangle
arecongruent.
Asquareisaparallelogramwhoseanglesarerightandallsidesarecongruent.
Arhombusisaparallelogramthathasallsidescongruent.Diagonalsof
arhombusareperpendicular.
Atrapeziumisaquadrilateralwithatleastonepairofparallelsides.Parallel
sidesoftrapeziumarecalledbases,nonparallelsidesarecalledlegs.
Atrapeziumwithcongruentlegsiscalledanisoscelestrapezium.
Atrapeziumwithonelegperpendiculartothebaseiscalledaright-angled
trapezium.Figure1.14ashowsvariouskindsoftrapeziums.
Adeltoidisaquadrilateralwhoseaxisofsymmetrypassesthroughoneof
diagonals.
AdeltoidisshowninFigure1.14b.Ithastwopairsofcongruentadjacentsi-
des.Diagonalsofadeltoidareperpendicular.
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