T H E E L E M E N T S	Book VI   Proposition 15
	But,     as CAB is to BAD,     so is CA to AD, [VI.1] and,     as EAD is to BAD,     so is EA to AB. [VI.1] Therefore also,     as CA is to AD,     so is EA to AB. [V.11] Therefore     in the triangles ABC, ADE the sides about the equal angles are reciprocally proportional.
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