— GEOMETOR • elements

G.9 figure

A figure is that which is contained by any boundary or boundaries.

A circle ( A B ) is a plane figure contained by one arc defined by a center A and a point B establishing its defining radius / A B /, such that all segments / A B /, / A C /, / A D / falling upon the arc from A are equal.

G.66 triangles on the same base in the same parallels

Triangles on the same base and in the same parallels are equal in area.

G.67 triangles on equal bases in the same parallels

Triangles on equal bases and in the same parallels are equal in area.

G.89 square of a difference

If a segment is cut at random, the sum of the squares on the whole and on one of the parts equals twice the rectangle contained by the whole and that part together with the square on the remaining part.

G.90 four rectangles plus square on difference

If a segment is cut at random, four times the rectangle contained by the whole and one of the parts together with the square on the remaining part equals the square on the whole and the first part as one segment.

G.96 semicircle

A semicircle is the figure contained by a diameter and the arc cut off by it.

G.122 sector of a circle

A:term:**sector of a circle** <sector-of-circle> is the:term:figure <G.9> which, when an:term:angle <G.22> is constructed at the:term:center <center> of the:term:circle <G.10>, is contained by the:term:segments <G.4> containing the angle and the arc cut off by them.

G.126 segment of a circle

A:term:**segment of a circle** <segment-of-circle> is the:term:figure <G.9> contained by a:term:segment <G.4> and a arc of a:term:circle <G.10>.

G.141 construct a circle segment on a chord admitting a given angle

On a given segment, construct a segment of a circle admitting an angle equal to a given rectilineal angle.

G.148 polygon inscribed in a circle

A:term:polygon <G.12> is said to be:term:**inscribed in a circle** <inscribed-in-circle> when each:term:angle <G.22> of the inscribed:term:figure <G.9> lies on the arc of the:term:circle <G.10>.

G.150 polygon circumscribed about a circle

A:term:polygon <G.12> is said to be:term:**circumscribed about a circle** <circumscribed-about-circle>, when each side of the circumscribed:term:figure <G.9> touches the arc of the:term:circle <G.10>.

G.152 polygon inscribed in a polygon

A:term:polygon <G.12> is said to be:term:**inscribed in a polygon** <inscribed-in-rectilineal-figure> when the respective:term:angles <G.22> of the inscribed:term:figure <G.9> lie on the respective sides of that in which it is inscribed.

G.153 circle inscribed in a polygon

Similarly a:term:circle <G.10> is said to be:term:**inscribed in a figure** <circle-inscribed-in-figure> when the arc of the circle touches each side of the:term:figure <G.9> in which it is inscribed.

G.155 polygon circumscribed about a polygon

Similarly a:term:figure <G.9> is said to be:term:**circumscribed about a figure** <circumscribed-about-figure> when the respective sides of the circumscribed figure pass through the respective:term:angles <G.22> of that about which it is circumscribed.

G.156 circle circumscribed about a polygon

A:term:circle <G.10> is said to be:term:**circumscribed about a figure** <G.155> when the arc of the circle passes through each:term:angle <G.22> of the:term:figure <G.9> about which it is circumscribed.

G.157 circumscribe a circle about a triangle

Circumscribe a circle about a given triangle.

G.160 inscribe a circle in a square

Inscribe a circle in a given square.

G.168 inscribe a regular pentadecagon in a circle

Inscribe an equilateral and equiangular fifteen-angled figure in a given circle.

G.209 height of a figure

The height of any:term:figure <G.9> is the:term:perpendicular <G.33> drawn from the vertex to the base.

G.220 cut similarly

Cut a given uncut segment similarly to a given cut segment.

G.229 describe on a given segment a rectilinear figure

Describe on a given segment a rectilinear figure similar and similarly situated to a given rectilinear figure.

G.231 similar triangles duplicate

Similar triangles are to one another in the duplicate ratio of the corresponding sides.

G.233 figures similar polygon

Figures which are similar to the same polygon are also similar to one another.

G.234 segments proportional polygons

If four segments be proportional, the polygons similar and similarly described upon them is proportional; and, if the polygons similar and similarly described upon them be proportional, the segments will themselves also be proportional.

G.236 parallelogram parallelograms diameter

In any parallelogram the parallelograms about the diameter are similar both to the whole and to one another.

G.237 construct one and the same figure similar to

Construct one and the same figure similar to a given polygon and equal to another given polygon.

G.239 parallelograms applied segment

Of all the parallelograms applied to the same segment and deficient by parallelogrammic figures similar and similarly situated to that described on the half of the segment, that parallelogram is greatest which is applied to the half of the segment and is similar to the defect.

G.240 segment apply parallelogram

To a given segment to apply a parallelogram equal to a given polygon and deficient by a parallelogrammic figure similar to a given one: thus the given polygon must not be greater than the parallelogram described on the half of the segment and similar to the defect.

G.241 segment apply parallelogram

To a given segment to apply a parallelogram equal to a given polygon and exceeding by a parallelogrammic figure similar to a given one.

G.243 extreme and mean ratio

Cut a given segment in extreme and mean ratio.

G.244 right angled triangles

In right-angled triangles the figure on the side subtending the right angle is equal to the similar and similarly described figures on the sides containing the right angle.

G.377 magnitudes ratio number

If two magnitudes have to one another the ratio which a number has to a number, the magnitudes is commensurable.

G.381 squares segments commensurable

The squares on segments commensurable in length have to one another the ratio which a square number has to a square number; and squares which have to one another the ratio which a square number has to a square number will also have their sides commensurable in length. But the squares on segments incommensurable in length have not to one another the ratio which a square number has to a square number; and squares which have not to one another the ratio which a square number has to a square number will not have their sides commensurable in length either.

G.388 incommensurable magnitudes added

If two incommensurable magnitudes be added together, the whole is incommensurable with each of them; and, if the whole be incommensurable with one of them, the original magnitudes is incommensurable.

G.389 there unequal segments

If there be two unequal segments, and to the greater there be applied a parallelogram equal to the fourth part of the square on the less and deficient by a square figure, and if it divide it into parts which are commensurable in length, then the square on the greater is greater than the square on the less by the square on a segment commensurable with the greater. And, if the square on the greater be greater than the square on the less by the square on a segment commensurable with the greater, and if there be applied to the greater a parallelogram equal to the fourth part of the square on the less and deficient by a square figure, it will divide it into parts which are commensurable in length.

G.390 there unequal segments

If there be two unequal segments, and to the greater there be applied a parallelogram equal to the fourth part of the square on the less and deficient by a square figure, and if it divide it into parts which are incommensurable, the square on the greater is greater than the square on the less by the square on a segment incommensurable with the greater. And, if the square on the greater be greater than the square on the less by the square on a segment incommensurable with the greater, and if there be applied to the greater a parallelogram equal to the fourth part of the square on the less and deficient by a square figure, it divides it into parts which are incommensurable.

G.407 find two segments incommensurable in square which make

Find two segments incommensurable in square which make the sum of the squares on them rational but the rectangle contained by them medial.

G.408 find two segments incommensurable in square which make

Find two segments incommensurable in square which make the sum of the squares on them medial but the rectangle contained by them rational.

G.434 area contained rational

If an area be contained by a rational segment and the first binomial, the “side” of the area is the irrational segment which is called binomial.

G.435 area contained rational

If an area be contained by a rational segment and the second binomial, the “side” of the area is the irrational segment which is called a first bimedial.

G.440 square binomial segment

The square on the binomial segment applied to a rational segment produces as breadth the first binomial.

G.443 square major segment

The square on the major segment applied to a rational segment produces as breadth the fourth binomial.

G.477 area contained rational

If an area be contained by a rational segment and a first apotome, the “side” of the area is an apotome.

G.478 area contained rational

If an area be contained by a rational segment and a second apotome, the “side” of the area is a first apotome of a medial segment.

G.479 area contained rational

If an area be contained by a rational segment and a third apotome, the “side” of the area is a second apotome of a medial segment.

G.480 area contained rational

If an area be contained by a rational segment and a fourth apotome, the “side” of the area is minor.

G.481 area contained rational

If an area be contained by a rational segment and a fifth apotome, the “side” of the area is a segment which produces with a rational area a medial whole.

G.482 area contained rational

If an area be contained by a rational segment and a sixth apotome, the “side” of the area is a segment which produces with a medial area a medial whole.

G.483 square apotome applied

The square on an apotome applied to a rational segment produces as breadth a first apotome.

G.484 square apotome medial

The square on a first apotome of a medial segment applied to a rational segment produces as breadth a second apotome.

G.485 square apotome medial

The square on a second apotome of a medial segment applied to a rational segment produces as breadth a third apotome.

G.486 square minor segment

The square on a minor segment applied to a rational segment produces as breadth a fourth apotome.

G.487 square segment produces

The square on the segment which produces with a rational area a medial whole, if applied to a rational segment, produces as breadth a fifth apotome.

G.496 medial area there

If from a medial area there be subtracted a medial area incommensurable with the whole, the two remaining irrational segments arise, either a second apotome of a medial segment or a segment which produces with a medial area a medial whole.

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.555 there pyramids height

If there be two pyramids of the same height which have triangular bases, and each of them be divided into two pyramids equal to one another and similar to the whole, and into two equal prisms, then, as the base of the one pyramid is to the base of the other pyramid, so will all the prisms in the one pyramid be to all the prisms, being equal in multitude, in the other pyramid.

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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