## Elements of Geometry, Containing the First Six Books of Euclid |

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### Common terms and phrases

abc is equal adjacent angles Algebra angle abc angle bac angle bcd angles equal base bc bisect centre circle abc circumference diameter double draw equal angles equal circles equal right lines equal to f equi equimultiples Euclid EUCLID'S ELEMENTS exceed exterior angle fore four magnitudes fourth Geometry given circle given point given rectilineal angle given right line gnomon greater ratio hence inscribed join less Let abc multiple opposite angle parallel parallelogram perpendicular polygon proportional q. e. d. Deductions q. e. d. PROPOSITION rectangle contained remaining angle right line ab right line ac right line drawn segment similar and similarly square of ac subtending Theorem three right lines tiple touches the circle triangle abc triangle def whence wherefore the angle whole

### Popular passages

Page 2 - A diameter of a circle is a straight line drawn through the centre, and terminated both ways by the circumference. XVIII. A semicircle is the figure contained by a diameter and the part of the circumference cut off by the diameter. XIX. "A segment of a circle is the figure contained by a straight line, and the circumference it cuts off.

Page 78 - The straight line drawn at right angles to the diameter of a circle, from the extremity of it, falls without the circle...

Page 37 - The complements of the parallelograms, which are about the diameter of any parallelogram, are equal to one another.

Page 152 - If two triangles have one angle of the one equal to one angle of the other and the sides about these equal angles proportional, the triangles are similar.

Page 31 - And because the angle ABC is equal to the angle BCD, and the angle CBD to the angle ACB, therefore the whole angle ABD is equal to the whole angle ACD • (ax.

Page 12 - To bisect a given finite straight line, that is, to divide it into two equal parts. Let AB be the given straight line : it is required to divide it intotwo equal parts.

Page 77 - DH; (I. def. 15.) therefore DH is greater than DG, the less than the greater, which is impossible : therefore no straight line can be drawn from the point A, between AE and the circumference, which does not cut the circle : or, which amounts to the same thing, however great an acute angle a straight line makes with the diameter at the point A, or however small an angle it makes with AE, the circumference must pass between that straight line and the perpendicular AE.

Page 103 - To describe a square about a given circle. Let ABCD be the given circle ; it is required to describe a square about it. . Draw two diameters AC, BD of the circle ABCD, at right angles to one another, and through the points A, B, • 17.3. C, D, draw...

Page 11 - ... equal to them, of the other. Let ABC, DEF be two triangles which have the two sides AB, AC equal to the two sides DE, DF, each to each, viz. AB equal to DE, and AC to DF ; but the base CB greater than the base EF ; the angle BAC is likewise greater than the angle EDF.

Page 92 - From a given circle to cut off a segment, which shall contain an angle equal to a given rectilineal angle.