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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

## Euclid's Elements of Geometry: Chiefly from the Text of Dr. Simson, with ...

Robert Potts - 1868 - 410 pages
...BD, the common section of the planes AB, BC, cannot but be a straight line. PROPOSITION IV. THEOREM. 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: With Practical Applications to Mensuration

Benjamin Greenleaf - 1868 - 338 pages
...AB, A CD is a straight 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...

## The Edinburgh university calendar

Edinburgh univ - 1871
...for the base of a similar triangle whose area is threefourths of the former. 7. If a straight line be at right angles to each of two straight lines at their point of intersection, it is at right angles to their plane. 8. Prove the inequality — x* +y* + z*>xy + xz +yz. 9. Solve the...

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

William Chauvenet - Geometry - 1871 - 380 pages
...will be the required perpendicular. PROPOSITION 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...

## Elements of geometry, containing books i. to vi.and portions of books xi ...

Euclides, James Hamblin Smith - Geometry - 1872 - 349 pages
...MN. QED Note. — The Propositions which follow are numbered as in Euclid. PROPOSITION IV. THEOREM. If a straight line stand at right angles to each of two straight lines, at the point of their intersection, it must also be at right angles to the plane that passes through them....

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

William Chauvenet - Geometry - 1872 - 382 pages
...will be the required perpendicular. PROPOSITION 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...

## The Calendar of Owens college, Manchester

Manchester univ - 1872
...circle, one of these lines is equal to the sum of the other two. 6. 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. 7. Define parallel planes. Prove that two planes...

## The Elements of Euclid, containing the first six books, with a selection of ...

Euclides - 1874 - 342 pages
...AB and BC, must be in a straight line. Wherefore, if two planes, &c. QED PROPOSITION 4. — Theorem. If a straight line stand at right angles to each of two straight lines at. the point of their intersection, it is at right angles to the plane in which they are. Let the straight...

## Euclidian Geometry

Francis Cuthbertson - Euclid's Elements - 1874 - 349 pages
...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...

## Solutions of the Cambridge Senate-house Problems and Riders for the Year 1875

Sir George Greenhill - Mathematics - 1876 - 318 pages
...perpendiculars from B and D on FA are equal, and therefore FA bisects BD, and its parallel CE. •vi. 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...