— GEOMETOR • elements

G.502 part segment plane

A part of a segment cannot be in the plane of reference and a part in a plane more elevated.

G.503 segments cut plane

If two segments cut one another, they are in one plane, and every triangle is in one plane.

G.504 planes cut common

If two planes cut one another, their common section is a segment.

G.505 line at right angles to a plane

A:term:segment <G.4> is:term:**at right angles to a plane** <right-angles-to-plane>, when it makes:term:right angles <G.33> with all the segments which meet it and are in the:term:plane <G.7>.

G.506 segment set right

If a segment be set up at right angles to two segments which cut one another, at their common point of section, it is at right angles to the plane through them.

G.507 segment set right

If a segment be set up at right angles to three segments which meet one another, at their common point of section, the three segments are in one plane.

G.508 segments right angles

If two segments be at right angles to the same plane, the segments is parallel.

G.509 segments parallel points

If two segments be parallel and points be taken at random on each of them, the segment joining the points is in the same plane with the parallel lines.

G.510 segments parallel right

If two segments be parallel, and one of them be at right angles to any plane, the remaining one is at right angles to the same plane.

G.511 straight lines parallel

Straight lines which are parallel to the same segment and are not in the same plane with it are also parallel to one another.

G.512 segments meeting parallel

If two segments meeting one another be parallel to two segments meeting one another not in the same plane, they will contain equal angles.

G.513 elevated point draw

From a given elevated point to draw a segment perpendicular to a given plane.

G.514 set segment right

To set up a segment at right angles to a given plane from a given point in it.

G.515 point segments set

From the same point two segments cannot be set up at right angles to the same plane on the same side.

G.516 parallel planes

Parallel planes are those which do not meet.

G.517 planes segment right

Planes to which the same segment is at right angles is parallel.

G.518 segments meeting parallel

If two segments meeting one another be parallel to two segments meeting one another, not being in the same plane, the planes through them are parallel.

G.519 parallel planes cut

If two parallel planes be cut by any plane, their common sections are parallel.

G.520 segments cut parallel

If two segments be cut by parallel planes, they is cut in the same ratios.

G.521 plane at right angles to a plane

A:term:**plane is at right angles to a plane** <plane-at-right-angles-to-plane> when the:term:segments <G.4> drawn, in one of the:term:planes <G.7>,:term:at right angles <G.33> to the common section of the planes are at right angles to the remaining plane.

G.522 segment right angles

If a segment be at right angles to any plane, all the planes through it is at right angles to the same plane.

G.523 planes cut right

If two planes which cut one another be at right angles to any plane, their common section is at right angles to the same plane.

G.524 solid angle

A:term:**solid angle** <solid-angle> is the inclination constituted by more than two:term:lines <G.2> which meet one another and are not in the same:term:surface <G.533>, towards all the lines. Otherwise: A:term:**solid angle** <solid-angle> is that which is contained by more than two:term:plane angles <G.22> which are not in the same:term:plane <G.7> and are constructed to one:term:point <G.1>.

G.525 solid angle contained

If a solid angle be contained by three plane angles, any two, taken together in any manner, are greater than the remaining one.

G.526 solid angle contained

Any solid angle is contained by plane angles less than four right angles.

G.527 there plane angles

If there be three plane angles of which two, taken together in any manner, are greater than the remaining one, and they are contained by equal segments, it is possible to construct a triangle out of the segments joining the extremities of the equal segments.

G.528 construct a solid angle out of three plane

Construct a solid angle out of three plane angles two of which, taken together in any manner, are greater than the remaining one: thus the three angles must be less than four right angles.

G.529 solid

A:term:**solid** <solid> is that which has length, breadth, and depth.

G.530 solid contained parallel

If a solid be contained by parallel planes, the opposite planes in it are equal and parallelogrammic.

G.531 parallelepipedal solid cut

If a parallelepipedal solid be cut by a plane which is parallel to the opposite planes, then, as the base is to the base, so will the solid be to the solid.

G.532 segment point construct

On a given segment, and at a given point on it, to construct a solid angle equal to a given solid angle.

G.533 extremity of a solid

An:term:extremity <G.6> of a:term:solid <G.529> is a:term:**surface** <surface>.

G.534 similar solid figures

Similar solid figures are those:term:contained by similar planes <G.533> equal in multitude.

G.535 equal and similar solid figures

Equal and similar solid figures are those:term:contained by similar planes <G.533> equal in multitude and in magnitude.

G.536 describe on a given segment a parallelepipedal solid

Describe on a given segment a parallelepipedal solid similar and similarly situated to a given parallelepipedal solid.

G.537 prism

A:term:**prism** <prism> is a:term:solid figure <G.529> contained by:term:planes <G.7> two of which, namely those which are opposite, are equal, similar and:term:parallel <G.52>, while the rest are parallelograms.

G.538 parallelepipedal solid cut

If a parallelepipedal solid be cut by a plane through the diagonals of the opposite planes, the solid is bisected by the plane.

G.539 parallelepipedal solids base

Parallelepipedal solids which are on the same base and of the same height, and in which the extremities of the sides which stand up are on the same segments, are equal.

G.540 parallelepipedal solids base

Parallelepipedal solids which are on the same base and of the same height, and in which the extremities of the sides which stand up are not on the same segments, are equal.

G.541 parallelepipedal solids equal

Parallelepipedal solids which are on equal bases and of the same height are equal.

G.542 parallelepipedal solids height

Parallelepipedal solids which are of the same height are to one another as their bases.

G.543 similar parallelepipedal solids

Similar parallelepipedal solids are to one another in the triplicate ratio of their corresponding sides.

G.544 equal parallelepipedal solids

In equal parallelepipedal solids the bases are reciprocally proportional to the heights; and those parallelepipedal solids in which the bases are reciprocally proportional to the heights are equal.

G.545 there equal plane

If there be two equal plane angles, and on their vertices there be set up elevated segments containing equal angles with the original segments respectively, if on the elevated segments points be taken at random and perpendiculars be drawn from them to the planes in which the original angles are, and if from the points so arising in the planes segments be joined to the vertices of the original angles, they will contain, with the elevated segments, equal angles.

G.546 segments proportional parallelepipedal

If three segments be proportional, the parallelepipedal solid formed out of the three is equal to the parallelepipedal solid on the mean which is equilateral, but equiangular with the aforesaid solid.

G.547 segments proportional parallelepipedal

If four segments be proportional, the parallelepipedal solids on them which are similar and similarly described is proportional; and, if the parallelepipedal solids on them which are similar and similarly described be proportional, the segments will themselves also be proportional.

G.548 cube

A:term:**cube** <cube> is a:term:solid figure <G.529> contained by six equal:term:squares <G.63>.

G.549 sides opposite planes

If the sides of the opposite planes of a cube be bisected, and planes be carried through the points of section, the common section of the planes and the diameter of the cube bisect one another.

G.550 there prisms equal

If there be two prisms of equal height, and one have a parallelogram as base and the other a triangle, and if the parallelogram be double of the triangle, the prisms is equal.

G.553 pyramid

A:term:**pyramid** <pyramid> is a:term:solid figure <G.529>, contained by:term:planes <G.7>, which is constructed from one plane to one:term:point <G.1>.

G.561 cone

When, one side of those about the:term:right angle <G.33> in a:term:right-angled triangle <G.78> remaining fixed, the:term:triangle <G.12> is carried round and restored again to the same position from which it began to be moved, the:term:figure <G.9> so comprehended is a:term:**cone** <cone>. And, if the:term:segment <G.4> which remains fixed equals the remaining side about the right angle which is carried round, the cone is:term:**right-angled** <right-angled-cone>; if less,:term:**obtuse-angled** <obtuse-angled-cone>; and if greater,:term:**acute-angled** <acute-angled-cone>.

G.562 cylinder

When, one side of those about the:term:right angle <G.33> in a:term:rectangular parallelogram <G.81> remaining fixed, the parallelogram is carried round and restored again to the same position from which it began to be moved, the:term:figure <G.9> so comprehended is a:term:**cylinder** <cylinder>.

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