Trapezoid - Wikipedia
What is a Quadrilateral? (Definition, Properties & Shapes) // Tutors.com
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geometry - $ABCD$ is a convex quadrilateral. If $\angle BAC=10°$, $\angle CAD=40°$, $\angle ADB=50°$, $\angle BDC=20°$, then find $\angle CBD$. - Mathematics Stack Exchange
Irregular Convex Quadrilateral Calculator
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Quadrilateral Calculator
I have the four sides of an irregular quadrilateral and none of its angles. How can I calculate its area? - Quora
Convex quadrilateral; Area and parallel sides - Mathematics Stack Exchange
Area of convex quadrilateral – GeoGebra
area of a convex quadrilateral using the diagonals - YouTube
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Quadrilateral -- from Wolfram MathWorld
Online calculator: Area of a convex quadrilateral. Example of creating a calculator.
Irregular Convex Quadrilateral Calculator
geometry - Figuring out angles and lengths of irregular quadrilateral - Mathematics Stack Exchange
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