مخطط مرجعي
Here we use the notations in the figure to the right. Area of the cyclic quadrilateral = Area of + Area of
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But since is a cyclic quadrilateral, Hence Therefore
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Solving for common side DB, in ADB and BDC, the law of cosines gives
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Substituting (since angles and are supplementary) and rearranging, we have
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Substituting this in the equation for the area,
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which is of the form and hence can be written as
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which, regrouping, is of the form
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hence yielding four linear factors:
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Introducing
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Taking the square root, we get
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