ABCD is a non-convex quadrilateral. The points P, Q, R and S
are the midpoints of the edges of ABCD. You can change the shape of
the quadrilateral ABCD.

What do you notice about the quadrilateral PQRS and its area as ABCD changes?

If you say that what you have noticed is always true, then you are making a conjecture. Can you prove your conjecture?

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Angles - points, lines and parallel lines. Area - triangles, quadrilaterals, compound shapes. Circle properties and circle theorems. Making and proving conjectures. Dynamic geometry. Sine, cosine, tangent. Quadrilaterals. Regular polygons and circles. Mathematical reasoning & proof. Interactivities.