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If a straight line is perpendicular to each of two other straight lines at their point of intersection, it is perpendicular to the plane of the two lines.
The Elements of Solid Geometry - Page 4
by William C. Bartol - 1893 - 95 pages

## Plane and Solid Geometry: To which is Added Plane and Spherical Trigonometry ...

George Roberts Perkins - Geometry - 1856 - 460 pages
...planes is in a straight line. THEOREM Iv. If a straight line is perpendicular to each of two straight lines at their point of intersection^ it is perpendicular to the plane of these lines. Let AP be perpendicular to the two lines PB, PC, at their point of intersection P ; then...

## Plane and Solid Geometry: To which is Added Plane and Spherical Trigonometry ...

George Roberts Perkins - Geometry - 1860 - 468 pages
...planes is in a straight line. THEOREM IV. If a straight line is perpendicular to each of two straight lines at their point of intersection, it is perpendicular to the plane of these lines. Let AP be perpendicular to the two* lines PB, PC, at their point of intersection P ; then...

## Elements of Geometry and Trigonometry: With Practical Applications

Benjamin Greenleaf - Geometry - 1862 - 520 pages
...line. PROPOSITION IV. — THEOREM. 401. If a straight line is perpendicular to each of two straight lines, at their point of intersection, it is perpendicular to the plane in which the two lines lie. Let the straight line AB be perpendicular to each of the straight lines...

## Elements of Plane and Spherical Trigonometry: With Practical Applications

Benjamin Greenleaf - Geometry - 1861 - 628 pages
...line. PROPOSITION IY. — THEOREM. 401. If a straight line is perpendicular to each of two straight lines, at their point of intersection, it is perpendicular to the plane in which the two lines lie. Let the straight line AB be perpendicular to each of the straight lines...

## Elements of Geometry and Trigonometry

Adrien Marie Legendre - Geometry - 1863 - 464 pages
...which was to be proved. PROPOSITION IY. THEOREM. If a straight line is perpendicular to two straight lines at their point of intersection, it is perpendicular to the plane of those lines. AP be perpendicular to every line of the plane which pusses through P, and consequently,...

## Elements of Geometry: With Practical Applications to Mensuration

Benjamin Greenleaf - Geometry - 1863 - 504 pages
...B 1> PROPOSITION IV. — THEOREM. 401. If a straight line is pcrpemlicular to each of two straight lines, at their point of intersection, it is perpendicular to the plane in which the two lines lie. Let the straight line AB be perpendicular to each of the straight lines...

## Elements of Geometry: With Practical Applications to Mensuration

Benjamin Greenleaf - Geometry - 1868 - 338 pages
...line. PROPOSITION IV. — THEOREM. 401. If a straight line is perpendicular to each of two straight lines, at their point of intersection, it is perpendicular to the plane in which the two lines lie. Let the straight line AB be perpendicular to each of the straight lines...

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

William Chauvenet - Geometry - 1871 - 380 pages
...V.— THEOREM. / / • • '"( ' ' 13. 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. Let AP be perpendicular to PB and PC, at their intersection P; then, AP is perpendicular...