T H E E L E M E N T S |
Book III Proposition 31 | |
Therefore the whole angle BAC is equal to the two angles ABC, ACB. But the angle FAC exterior to the triangle ABC is also equal to the two angle ABC, ACB; [I.32] therefore the angle BAC is also equal to the angle FAC; therefore each is right; [I.Def.10] therefore the angle BAC in the semicircle BAC is right. Being what it was required to prove. |
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