The straight line drawn at right angles to the diameter of a circle from its end will fall outside the circle, and into the space between the straight line and the circumference another straight line cannot be interposed, further the angle of the semicircle is greater, and the remaining angle less, than any acute rectilinear angle.
Corollary
From this it is clear that the straight line drawn at right angles to the diameter of a circle from its end touches the circle.
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