Explanation:
Quadrilateral

Six different types of quadrilaterals

Edges and Vertices

4



Internal angles (degrees)

90° (for square)

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 (5sided), hexagon (6sided) and so on. The word quadrilateral is made of the words quad (meaning "four") and lateral (meaning "of
sides").The interior angles of a simple quadrilateral add up to 360 degrees of arc
http://en.wikipedia.org/wiki/Quadrilateral
The sum of
the lengths of any two sides of a triangle always exceeds the length of the
third side, a principle known as the triangle inequality. (Our solved example in mathguru.com uses this concept)
Since the
vertices of a triangle are assumed to be noncollinear, it is not possible for
the sum of the length of two sides be equal to the length of the third side.
http://en.wikipedia.org/wiki/Triangle
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