“If a straight line is perpendicular to each of two straight lines at their point of intersection it is perpendicular to the plane of those lines.”
Arthur Latham Baker The Elements of Solid Geometr with Numerous Exercises (Boston, MA: Ginn & Company, 1893)
2400×1454, 322.9 KiB
1024×620, 35.1 KiB
640×387, 19.3 KiB
320×193, 8.3 KiB