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If a straight line stand at right angles to each of two straight lines at the point of their intersection, it shall also be at right angles to the plane which passes through them, that is, to the plane in which they are.
Euclid's Elements: Or, Second Lessons in Geometry,in the Order of Simson's ... - Page 133
by Dennis M'Curdy - 1846 - 138 pages

## The First Six, and the Eleventh and Twelfth Books of Euclid's Elements: With ...

Euclid, James Thomson - Geometry - 1845 - 380 pages
...cannot but be a straight line.* Therefore, &c. Puor. IV. THEOR. — If a straight line be perpendicular to each of two straight lines at their point of intersection, it is also perpendicular to the plane in which they are. Let the straight lineEF be perpendicular to each...

## A system of practical mathematics; being no.xvi. of a new series of school-books

Scottish school-book assoc - 1845 - 434 pages
...common section of the two planes is a straight line. GEOMETRY OF PLANES. PBOPOSITION LXXX — THEOREM. If a straight line stand at right angles to each of two traight lines in the point of their intersection, it will also e at right angles to the plane in which...

## Elements of Geometry: Containing the First Six Books of Euclid, with a ...

John Playfair - Euclid's Elements - 1846 - 332 pages
...therefore common to the planes AB and BC, or it is the common sectioa of these planes. PROP. IV. THEOR. If a straight line stand at right angles to each of two straight lines in the point of their intersection, it will also be at right angles to the plane in which these lines...

## The Elements of Euclid, the parts read in the University of Cambridge [book ...

Euclides - 1846 - 292 pages
...planes AB, BC, cannot but be a straight line. Wherefore, If two planes %c. ct. KD PROP. IV. THEOR. If a straight line stand at right angles to each of two straight lines in the point of their intersection, it shall also be at right angles to the plane which passes through...

## The Mechanic's Magazine, Museum, Register, Journal and Gazette, Volume 44

1846
...too, by Euclid with an elegance fully equal to that by which any other author has proved it,) that "if a straight line stand at right angles to each of two stright lines at their point of intersection, it shall also be at right angles to every other line...

## Iron: An Illustrated Weekly Journal for Iron and Steel ..., Volume 44

...too, by Euclid with an elegance fully equal to that by which any other author has proved it,) that "if a straight line stand at right angles to each of two stright lines at their point of intersection, it shall also be at right angles to every other line...

## An elementary course of mathematics, Volume 2

Samuel Hunter Christie - 1847 - 172 pages
...section of the planes AB, BC, cannot but be a straight line: which was to be proved. PROP. IV. THEOR. If a straight line stand at right angles to each of two straight lines in the point of their intersection, it shall also be at right angles to the plane which passes through...

## Elements of Geometry and Conic Sections

Elias Loomis - Conic sections - 1849 - 252 pages
...common section. Hence, if two planes, &c. 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. Through B draw any line BG, in the plane MN;...