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Example:Find Missing Angle in Quadrilateral.

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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. (Our solved example in mathguru.com uses this concept)


This is a special case of the n-gon interior angle sum formula (n - 2)180°. In a crossed quadrilateral, the interior angles on either side of the crossing add up to 720°.



Six different types of quadrilaterals

Edges and vertices


Schläfli symbol

{4} (for square)

Internal angle (degrees)

90° (for square)





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.