Text-book of Euclid's elements for the use of schools : books I - VI and XI (1900)
Hall, H. S. (Henry Sinclair), 1848-1934, Stevens, F. H. (Frederick Haller), 1853-1933 · MacMillan : London · leaf 431
relations which two or more planes bear toone another. Unless the contrary is stated the straightlines are supposed to be of indefinite length, and the planesof infinite extent. Solid geometry then proceeds to discuss the propertiesof solid figures, of surfaces which are not planes, and oflines… … Note. It will be proved in Proposition 4 that if a straight lineis perpendicular to two straight lines which meet it in a plane, it isalso perpendicular to every straight line which meets it in that plane. A straight line drawn perpendicular to a plane is said to be anormal to that plane. 2. The…
Geometry · Mathematics
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