T H E E L E M E N T S |
Book III Proposition 31 | |
This is at once manifest. For, since the angle contained by the straingt lines BA, AC is right, the angle contained by the circumference ABC and the straight line AC is greater than a right angle. Again, since the angle contained by the straight lines AC, CF is right, the angle contained by the straight line CA and the circumference ADC is less than a right angle. Further being what it was required to prove. |
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