 | Robert Potts - 1868 - 434 pages
...plane BC with the third plane. And because the plane AB is perpendicular to the third plane, and DE is drawn in the plane AB at right angles to AD, their common section, DE is perpendicular to the third plane. (XI. def. 4.) In the same manner, it may be proved, that DF... | |
 | Euclides - 1874 - 342 pages
...the third plane. Demonstration. Because the plane AB is perpendicular to the third plane, and DE is drawn in the plane AB at right angles to AD, their common section ; therefore 1. DE is perpendicular to the third plane (XI. Def. 4). In the same manner, it may be proved that DF... | |
 | 562 pages
...the plane to the plane." But, since AB is perpendicular to the plane MN, it is perpendicular to in it. Therefore the angle ABF is a right angle ; whence...therefore DE is at right angles to the plane of reference. Similarly we can prove that JDF is also at right angles to the plane of reference. Therefore from the... | |
| |
And because the plane AB is perpendicular to the third plane, and DE is drawn in the plane AB at right angles to AD their common section... 
