A quarter circle with two chords of given length. What is the area of the orange quadrilateral?
The quarter trampoline

A quarter circle with two chords of given length. What is the area of the orange quadrilateral?
A circle with an inscribed quadrilateral. Prove that ab=cd. Kindly provided by Marshall W. Buck.
A quadrilateral with connected side midpoints. What’s blue : red : yellow?
A rectangle with four line segments. What’s brown : blue?
An isosceles triangle and an external point with three line segments. Prove that the red points form a cyclic quadrilateral.
A cyclic quadrilateral with its diagonals and two altitudes. Prove that AB is parallel to EF.
Three circles with their centres and a triangle ABC. Given that D is the midpoint of BC, prove that quadrilateral ABEF and triangle ECF have both equal perimeter and equal area.
Three congruent triangles constitute a quadrilateral. What’s red : blue?
A cyclic quadrilateral with extended sides and two tangents forming an angle γ. What is γ in terms of α and β?
Two triangles form a quadrilateral. What’s the total orange area?