*You may wish to try the problem Bendy Quad first.*

Four rods are hinged at their ends to form a quadrilateral with fixed side lengths.

Show that the quadrilateral has a maximum area when it is cyclic.

Vectors. Creating and manipulating expressions and formulae. Quadrilaterals. Maximise/minimise/optimise. Mathematical reasoning & proof. Pythagoras' theorem. Circle properties and circle theorems. Area - triangles, quadrilaterals, compound shapes. Sine rule & cosine rule. Sine, cosine, tangent. Graphs.