| 1. | Equality holds if and only if the quadrilateral is a square.
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| 2. | Hence that point is the Fermat point of a convex quadrilateral.
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| 3. | Where and are the lengths of the diagonals of the quadrilateral.
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| 4. | A Lambert quadrilateral in the hyperbolic plane has 3 right angles.
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| 5. | The Quadrilateral was captured by the 6th Division on 18 September.
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| 6. | The proof as written is only valid for simple cyclic quadrilaterals.
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| 7. | This means that their dual polyhedra will have all quadrilateral faces.
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| 8. | Each settlement was built with a quadrilateral, uniform street grid.
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| 9. | The quadrilateral basis is encased by four slabs of white marble.
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| 10. | All triangles have an incircle, but not all quadrilaterals do.
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