The second shape is not a cyclic quadrilateral. One corner does not touch the circumference. The opposite angles in a cyclic quadrilateral add up to 180°.

The second shape is not a cyclic quadrilateral. One vertex does not touch the circumference. The opposite angles in a cyclic quadrilateral add up to 180°.

Surprisingly, when the quadrilateral is a parallelogram, like in a scissor lift, or “cyclic”, when the endpoints lie on a circle, the bar framework can move. Tweaking the ratios of the middle ...