Stage: 4 Challenge Level: 
This only uses the result that the area of a triangle is half the base times the height but you need to consider different cases according to whether the quadrilateral is convex or concave.
Stage 5 needs dealing with. Scale factors. Inscribed circle. Cyclic. Perimeters. Quadrilaterals. Similarity. Area. Circle theorems. Stage 5 - Reviewed 2012.
Published October 2002.
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