Stage: 4 Challenge Level: 
Prove that the area of a quadrilateral is given by half the product of the lengths of the diagonals multiplied by the sine of the angle between the diagonals.
Perimeters. Scale factors. Circle theorems. Stage 5 - Reviewed 2012. Quadrilaterals. Stage 5 needs dealing with. Cyclic. Area. Inscribed circle. Similarity.
Published October 2002.
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