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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.
Elements of Geometry: With Practical Applications to Mensuration - Page 170
by Benjamin Greenleaf - 1868 - 320 pages

## Elements of Geometry and Trigonometry: From the Works of A.M. Legendre

Adrien Marie Legendre - Geometry - 1874 - 512 pages
...straight line ; which was to be proved. PROPOSITION IV. THEOREM. Jf a straight line is perpendicular to two straight lines at their point of intersection, it is perpendicular to the plane of those lines. Let JOT be the plane of the two lines BB, (7(7, and let AP be perpendicular to these...

## Euclidian Geometry

Francis Cuthbertson - Euclid's Elements - 1874 - 400 pages
...DEFINITION. A straight line is said to be perpendicular to a plane PROPOSITION VI. . If a straight line be perpendicular to each of two straight lines at their point of intersection, it shall be perpendicular to the plane passing through them. Let PQ be j . to QA and QC. Then shall PQ...

## A Treatise on Elementary Geometry: With Appendices Containing a Collection ...

William Chauvenet - Geometry - 1875 - 468 pages
...will be the required perpendicular. PROPOSITION V.—THEOREM. 13. If a etraight line isperpendicular to each of two straight lines at their point of intersection., it is perpendicular to the plane of Uiose lines. Let AP be perpendicular to PR and PC, at their intersection P; then, AP is perpendicular...

## A Treatise on Elementary Geometry: With Appendices Containing a Collection ...

William Chauvenet - Geometry - 1875 - 390 pages
...these points; the straight line AP will be the required perpendicular. PROPOSITION V.— THEOREM. ^ 13. If a straight line is perpendicular to each of two straight lines at thttir point of intersection, it is perpendicular to the plane of those lines. Let AP be perpendicular...

## Annual Statement, Volumes 11-20

1876 - 646 pages
...area will be a maximum when these sides are at right angles. II.— SOLID AND SPHERICAL GEOMETRY. 7. If a straight line is perpendicular to each of two...of intersection, it is perpendicular to the plane of these lines. 8. Define symmetrical polyhedral angles. Illustrate the definition by a figure. 9....

## Manual of Geometry and Conic Sections: With Applications to Trigonometry and ...

William Guy Peck - Conic sections - 1876 - 394 pages
...a plane. PROPOSITION III. THEOREM. If a straight line is perpendicular to each of two intersecting lines at their point of intersection, it is perpendicular to the plane of those lines. Let AQ and DQ be two lines in the plane KL, and let PQ be perpendicular to both ; then...

## Elements of Geometry, Conic Sections, and Plane Trigonometry

Elias Loomis - Geometry - 1877 - 458 pages
...is their common section. Hence, if two planes, etc. PROPOSITION IV. THEOREM. If a straight line be perpendicular to each of two straight lines at their point of intersection, it will be perpendicular to the plane in which these lines are. Let the straight line AB be perpendicular...

## Elements of Descriptive Geometry

J. B. Millar - Geometry, Descriptive - 1878 - 264 pages
...planes out one another, their common section is a straight line 2 Theorem III. If a straight line be perpendicular to each of two straight lines at their point of intersection, it shall also be perpendicular to their plane 3 Theorem IV. Every plane which contains the normal to another...