...perpendicular, is at right angles to the line of the plane. ELEMENTARY GEOMETRY [CHAP. VI 407. COROLLARY II. If one of two parallel lines is perpendicular to a plane, the other is also. For, if not, at its point of intersection with the plane erect a perpendicular. This lies in a plane...

...in this plane. But AB and CD are both J_ to BD. Therefore, AB and CD are parallel. § 508 § 492 § 501 § 104 QED 520. COR. 1. If one of two parallel...For if through any point O of CD a line is A c drawn J_ to MN, it is II to AB (§ 519), and CD Mf . coincides with this -L and is -L to MN. § 105 521....

...this plane. But AB and CD are both _L to BD. Therefore, AB and CD are parallel. § 518 §508 § 492 §501 §104 QED 520. COR. 1. If one of two parallel...perpendicular to the plane. For if through any point 0 of CD a line is drawn _L to MN, it is il to AB (§ 519), and CD Mr coincides with this J_ and is...

...point in AB, draw AD. Draw BD, and through D, draw EF in the plane MN± to BD. § 518 § 508 § 492 §501 § 104 QED 520. COR. 1. If one of two parallel...plane. For if through any point O of CD a line is * fl drawn -L to MN, it is II to AB (§ 519), and CD coincides with this -L and is -L to MN. § 105...

...and CD are in the same plan**. But AB and CD are ± and CD are (Why?) Art. 505. Art. 121. QED 525. COR. 1. If one of two parallel lines is perpendicular to a plane, the other is perpendicular to the plane also. For, if AB and CD be ||. and AB J. plane PQ, a line drawn from C _L...

...the same plane. (Why?) But AB and CD are J_ 727). Art. 505. /. AB and CD are ||. Art. 121. QE D, 525, COR. 1. If one of two parallel lines -is perpendicular to a plane, the oilier ix perpendicular to the plane also. For, if AB and CD be ||, and AB _L Plane P#, a line drawn...

...projection of the third perpendicular on the plane of the given lines. XXI. G. If one of two parallels is perpendicular to a plane, the other is also perpendicular to the plane, and conversely. 0 T ' ,' .'E Q Hyp. If AB II CE, and AB is perpendicular to plane MQ, Cone. : then...

...the extremities of a given straight line ? SOLID GEOMETRY — BOOK VI PROPOSITION VIII. THEOREM 534 If one of two parallel lines is perpendicular to a...plane, the other is also perpendicular to the plane. N HYPOTHESIS. AB is || to CD, and AB is _L to the plane MN at B. CONCLUSION. CDisJ-toMN. PROOF Let...

...the extremities of a given straight line ? SOLID GEOMETRY— BOOK VI PROPOSITION VIII. THEOREM 534 If one of two parallel lines is perpendicular to a...plane, the other is also perpendicular to the plane. § 117 HYPOTHESIS. AB is || to CD, and AB is -L to the plane MH at B. CONCLUSION. CD is ± to MH. PROOF...

...any point in the perpendicular, the line so drawn is perpendicular to • the line of the plane. 9. If one of two parallel lines is perpendicular to a plane the other is also. 10. Two lines perpendicular to the same plane are parallel. Cor. Two straight lines both parallel to...