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 443
plane. I. Def. 7. And because B and D are two points in the plane CY, .*. the st. line joining B, D lies in that plane. Hence the st. line BD lies in both planes, and is therefore their common section. That is, the common section of the two planes is a straight line. Q.E.D. 422 EUCLIDS ELEMENTS.… … Let the straight line AD be perp. to each of the st. linesAB, AC at A their point of intersection. Then shall AD be perp. to the plane in which AB and AC lie. Produce DA to F, making AF equal to DA. Draw any st. line BC in the plane of AB, AC, to cutAB, AC at B and C; and in the same plane draw…
Geometry · Mathematics
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