T H E E L E M E N T S	Book IV   Proposition 9
	Now, since DA is equal to AB, and AC is common, therefore     the two sides DA, AC are equal to the two sides BA, AC; and the base DE is equal to the base BC; therefore     the angle DAC is equal to the angle BAC. [I.8] Therefore     the angle DAB is bisected by AC. Similarly     we can prove that each of the angles ABC, BCD, CAD is bisected by the straight lines AC, DB.
	Previous Page    Return to Propositions    Next Page