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.
Cyclic. Mathematical reasoning & proof. Circle theorems. Scale factors. Quadrilaterals. Fractal. Perimeters. Area. Similarity. Inscribed circle.
Published October 2002.
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