Quadrilateral
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Six different types of quadrilaterals
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Edges and Vertices
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4
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In Euclidean plane
geometry, a quadrilateral is a polygon with four sides (or 'edges') and four vertices or corners.
Sometimes, the term quadrangle is
used, by analogy with triangle,
and sometimes tetragon for consistency with pentagon (5-sided), hexagon (6-sided) and so on. The word quadrilateral is made of the words quad (meaning "four") and lateral (meaning "of sides").
Quadrilaterals are simple (not self-intersecting) or complex (self-intersecting), also called
crossed. Simple quadrilaterals are either convex or concave.
The interior angles of a simple quadrilateral add up to
360 degrees of arc.
http://en.wikipedia.org/wiki/Quadrilateral
The above explanation is copied from
Wikipedia, the free encyclopedia and is remixed as
allowed under the Creative Commons Attribution- ShareAlike
3.0 Unported License.
(Our solved example in mathguru.com also uses the below concept.
This is our own explanation, it is not taken from Wikipedia.)

To construct a quadrilateral
when 2 adjacent sides( x units, y units) and 3 angles(say 105
, 105
, 60
) are
known
• Draw a line segment MO = x units
• Make an angle of 105
at O
• With O as the centre and radius y units, we mark an arc on the
ray OX
• Make an angle of 105
at R
• Make an angle of 60
at M
• Mark the point of intersection at R
• MORE is the required Quadrilateral