— GEOMETOR • elements

G.24 congruent triangles by SAS

Triangles with two sides and the included angle equal are congruent (SAS).

G.27 triangle with equal base angles is isosceles

If two angles of a triangle are equal, the sides subtending the equal angles are also equal.

G.28 uniqueness of triangle sides on a base

On the same segment and on the same side, there cannot be constructed two distinct triangles with both pairs of conterminous sides equal.

G.39 supplementary adjacent angles form a line

If two segments at a point on a line on opposite sides make adjacent angles summing to two right angles, the two segments are collinear.

G.44 greater angle is subtended by greater side

In any triangle, the greater angle is subtended by the greater side.

G.50 converse hinge theorem

If two triangles have two sides equal to two sides respectively, the one with the greater base has the greater included angle.

G.51 congruent triangles by ASA and AAS

Triangles with two angles and one corresponding side equal are congruent (ASA / AAS).

G.53 equal alternate interior angles imply parallel lines

If a transversal cutting two lines makes the alternate interior angles equal, the lines are parallel.

G.68 equal triangles on the same base are in the same parallels

Equal triangles on the same base and on the same side lie in the same parallels.

G.69 equal triangles on equal bases are in the same parallels

Equal triangles on equal bases and on the same side lie in the same parallels.

G.98 find the center of a circle

Find the center of a given circle.

G.99 chord of a circle lies within the circle

The segment joining any two points on the arc of a circle falls within the circle.

G.101 intersecting chords not through the center do not bisect

In a circle, two intersecting chords that do not both pass through the center do not bisect one another.

G.102 intersecting circles have distinct centers

Two intersecting circles do not have the same center.

G.104 touching circles have distinct centers

Two circles that touch one another do not have the same center.

G.105 distances to a circle from an eccentric diameter point

From an eccentric point on the diameter of a circle, the greatest segment to the arc passes through the center, the least is the remainder of the diameter, and segments nearer the center are greater than those more remote, with at most two equal segments on opposite sides.

G.106 distances to a circle from an exterior point

From a point outside a circle, of segments falling on the concave arc the greatest passes through the center and nearer ones are greater, while on the convex arc the least lies between the point and the diameter and nearer ones are less, with at most two equal segments.

G.108 two circles intersect in at most two points

A circle does not intersect another circle at more than two points.

G.109 line of centers of internally touching circles

If two circles touch one another internally, the line joining their centers passes through the point of contact.

G.110 line of centers of externally touching circles

If two circles touch one another externally, the segment joining their centers passes through the point of contact.

G.112 two circles touch at most at one point

A circle does not touch another circle at more than one point, whether internally or externally.

G.118 perpendicular at extremity of a diameter is tangent

The line drawn at right angles to the diameter of a circle from its extremity falls outside the circle, no other line can be interposed between it and the arc, and the angle of the semicircle is greater than any acute rectilineal angle.

G.120 radius to point of contact is perpendicular to tangent

If a line touches a circle, the segment joined from the center to the point of contact is perpendicular to the tangent.

G.121 perpendicular to tangent at contact passes through center

If a line touches a circle, the line drawn at right angles to the tangent from the point of contact passes through the center of the circle.

G.128 no two similar unequal circle segments on the same chord

On the same segment and on the same side of it, there cannot be constructed two similar and unequal segments of circles.

G.129 similar circle segments on equal chords are equal

Similar segments of circles on equal segments are equal to one another.

G.134 angles standing on equal arcs are equal

In equal circles, angles standing on equal arcs are equal to one another, whether they stand at the centers or at the circumferences.

G.188 magnitudes ratio greater

Of magnitudes which have a ratio to the same, that which has a greater ratio is greater; and that to which the same has a greater ratio is less.

G.199 magnitudes proportional separando

If magnitudes be proportional separando, they is proportional componendo.

G.216 triangles angle equal

If two triangles have one angle equal to one angle, the sides about other angles proportional, and the remaining angles either both less or both not less than a right angle, the triangles is equiangular and will have those angles equal, the sides about which are proportional.

G.238 parallelogram there taken

If from a parallelogram there be taken away a parallelogram similar and similarly situated to the whole and having a common angle with it, it is about the same diameter with the whole.

G.250 unequal numbers set

Two unequal numbers being set out, and the less being continually subtracted in turn from the greater, if the number which is left never measures the one before it until an unit is left, the original numbers is prime to one another.

G.251 numbers prime find

Given two numbers not prime to one another, to find their greatest common measure.

G.252 numbers prime find

Given three numbers not prime to one another, to find their greatest common measure.

G.274 least numbers ratio

The least numbers of those which have the same ratio with them measure those which have the same ratio the same number of times, the greater the greater and the less the less.

G.275 numbers prime least

Numbers prime to one another are the least of those which have the same ratio with them.

G.276 least numbers ratio

The least numbers of those which have the same ratio with them are prime to one another.

G.277 numbers prime number

If two numbers be prime to one another, the number which measures the one of them is prime to the remaining number.

G.278 numbers prime number

If two numbers be prime to any number, their product also is prime to the same.

G.282 numbers prime sum

If two numbers be prime to one another, the sum is prime to each of them; and, if the sum of two numbers be prime to any one of them, the original numbers is prime to one another.

G.284 prime number prime

Any prime number is prime to any number which it does not measure.

G.287 composite number measured

Any composite number is measured by some prime number.

G.289 many numbers please

Given as many numbers as we please, to find the least of those which have the same ratio with them.

G.290 numbers find least

Given two numbers, to find the least number which they measure.

G.291 numbers measure number

If two numbers measure any number, the least number measured by them will also measure the same.

G.292 numbers find least

Given three numbers, to find the least number which they measure.

G.295 find the number which is the least that

Find the number which is the least that will have given parts.

G.296 there many numbers

If there be as many numbers as we please in continued proportion, and the extremes of them be prime to one another, the numbers are the least of those which have the same ratio with them.

G.299 many ratios please

Given as many ratios as we please in least numbers, to find numbers in continued proportion which are the least in the given ratios.

G.303 there many numbers

If there be as many numbers as we please in continued proportion, and the first do not measure the second, neither will any other measure any other.

G.339 many numbers please

If as many numbers as we please beginning from an unit be in continued proportion, and the number after the unit be not square, neither will any other be square except the third from the unit and all those which leave out one. And, if the number after the unit be not cube, neither will any other be cube except the fourth from the unit and all those which leave out two.

G.342 many numbers please

If as many numbers as we please beginning from an unit be in continued proportion, by however many prime numbers the last is measured, the next to the unit is measured by the same.

G.343 many numbers please

If as many numbers as we please beginning from an unit be in continued proportion, and the number after the unit be prime, the greatest will not be measured by any except those which have a place among the proportional numbers.

G.344 number least measured

If a number be the least that is measured by prime numbers, it will not be measured by any other prime number except those originally measuring it.

G.346 numbers prime number

If two numbers be prime to one another, the second will not be to any other number as the first is to the second.

G.347 there many numbers

If there be as many numbers as we please in continued proportion, and the extremes of them be prime to one another, the last will not be to any other number as the first to the second.

G.348 numbers investigate whether

Given two numbers, to investigate whether it is possible to find a third proportional to them.

G.349 numbers investigate possible

Given three numbers, to investigate when it is possible to find a fourth proportional to them.

G.350 prime numbers more

Prime numbers are more than any assigned multitude of prime numbers.

G.361 odd number measure

If an odd number measure an even number, it will also measure the half of it.

G.362 odd number prime

If an odd number be prime to any number, it is prime to the double of it.

G.366 number half odd

If a number have its half odd, it is even-times odd only.

G.367 number continually doubled

If a number neither be one of those which are continually doubled from a dyad, nor have its half odd, it is both even-times even and even-times odd.

G.370 many numbers please

If as many numbers as we please beginning from an unit be set out continuously in double proportion, until the sum of all becomes prime, and if the sum multiplied into the last make some number, the product is perfect.

G.373 less unequal magnitudes

If, when the less of two unequal magnitudes is continually subtracted in turn from the greater, that which is left never measures the one before it, the magnitudes is incommensurable.

G.374 commensurable magnitudes find

Given two commensurable magnitudes, to find their greatest common measure.

G.375 commensurable magnitudes find

Given three commensurable magnitudes, to find their greatest common measure.

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.385 magnitudes commensurable incommensurable

If two magnitudes be commensurable, and the one of them be incommensurable with any magnitude, the remaining one is incommensurable with the same.

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.400 medial area exceed

A medial area does not exceed a medial area by a rational area.

G.416 binomial segment divided

A binomial segment is divided into its terms at one point only.

G.417 bimedial segment divided

A first bimedial segment is divided at one point only.

G.418 bimedial segment divided

A second bimedial segment is divided at one point only.

G.419 major segment divided

A major segment is divided at one and the same point only.

G.420 side rational plus

The side of a rational plus a medial area is divided at one point only.

G.421 side sum medial

The side of the sum of two medial areas is divided at one point only.

G.461 apotome only rational

To an apotome only one rational segment can be annexed which is commensurable with the whole in square only.

G.462 apotome medial segment

To a first apotome of a medial segment only one medial segment can be annexed which is commensurable with the whole in square only and which contains with the whole a rational rectangle.

G.463 apotome medial segment

To a second apotome of a medial segment only one medial segment can be annexed which is commensurable with the whole in square only and which contains with the whole a medial rectangle.

G.464 minor segment only

To a minor segment only one segment can be annexed which is incommensurable in square with the whole and which makes, with the whole, the sum of the squares on them rational but twice the rectangle contained by them medial.

G.465 segment produces rational

To a segment which produces with a rational area a medial whole only one segment can be annexed which is incommensurable in square with the whole segment and which with the whole segment makes the sum of the squares on them medial, but twice the rectangle contained by them rational.

G.466 segment produces medial

To a segment which produces with a medial area a medial whole only one segment can be annexed which is incommensurable in square with the whole segment and which with the whole segment makes the sum of the squares on them medial and twice the rectangle contained by them both medial and also incommensurable with the sum of the squares on them.

Posts tagged 'reductio-ad-absurdum'