T H E E L E M E N T S |
Book II Proposition 9 | |
Then, since AC is equal to CE, the angle EAC is also equal to the angle AEC. And, since the angle at C is right, the remaining angles EAC, AEC are equal to one right angle. [I.32] And they are equal; therefore each of the angles CEA, CAE is half a right angle. For the same reason each of the angles CEB, EBC is also half a right angle; therefore the whole angle AEB is right. |
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