Can you find a quadrilateral that is not manmade?

Anna Demers, Education field, Succubus Of Syllables AKA I paint with words. Answered Apr 14, 2012 · Author has 1.5k answers and 5.4m answer views. Rocks on a beach. The contours of a turtle shell. 240 Views · View Upvoters · promoted by Boomerang for Gmail · Ever wonder how your emails are coming across? read more

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Tangential quadrilateral: the four sides are tangents to an inscribed circle. A convex quadrilateral is tangential if and only if opposite sides have equal sums. Cyclic quadrilateral: the four vertices lie on a circumscribed circle. A convex quadrilateral is cyclic if and only if opposite angles sum to 180°. read more