T H E E L E M E N T S |
Book IV Proposition 13 | |
Therefore the angle CBF is equal to the angle CDF. And, since the angle CDE is double of the angle CDF, and the angle CDE is equal to the angle ABC, while the angle CDF is equal to the angle CBF; therefore the angle CBA is is also double of the angle CBF. Therefore the angle ABF is equal to the angle FBC; therefore the angle ABC has been bisected by the straight line BF. |
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