When a straight line standing on another straight line makes the adjacent angles equal to one another, each of the angles is called a right angle; and the straight line which stands on the other is called a perpendicular to it.
The Elements of Euclid: Viz. the First Six Books, with the Eleventh and ... - الصفحة 10
بواسطة Alexander Ingram - 1799 - عدد الصفحات: 351
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