T H E E L E M E N T S |
Book IV Proposition 9 | |
Now, since the angle DAB is equal to the angle ABC, and the angle EAB is half the angle DAB, and the angle EBA half the angle ABC, therefore the angle EAB is also equal to the angle ABC; so that the side EA is also equal to EB. [I.6] Similarly we can prove that each of the straight lines EA, EB is equal to each of the straight lines EC, ED. |
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