The elements of Euclid for the use of schools and colleges; comprising the first six books and portions of the eleventh and twelfth books; (1903)
Euclid, Todhunter, I. (Isaac), 1820-1884, ed. edt, Simson, Robert, 1687-1768, ed. edt · London; New York, Macmillan · leaf 14
straight line standing onanother straight line makes the adjacentangles equal to one another, each of theangles is called a right angle ; and the straightline which stands on the other is called aperpendicular to it. 11. An obtuse angle is an angle which isgreater than a right angle. 12. An acute… … BOOK I. DEFINITIONS.
Euclid's Elements · Geometry · Mathematics, Greek
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