# The elements of plane geometry (Google eBook)

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### Contents

 The Circle 9 Angles at the Centre and Sectors 16 Angles in Segments 37 Tangents 49 Two Circles 64 Inscribed and Circumscribed Figures 72 The Circle in Connection with Areas 87 Definitions 101
 Fundamental Geometrical Propositions 117 Definitions 125 Of Ratio and Proportion 127 Fundamental Geometrical Propositions 144 Proportion 151 Areas 169 Loci and Problems 184 Definitions 197

### Popular passages

Page 92 - CD are three sides of a regular pentagon inscribed in the circle OBC. Ex. 156. Describe an isosceles triangle having each of the angles at the base one-third of the vertical angle. •• : £x. 157. Divide a right angle into five equal parts. Ex. 158. Shew that each diagonal of a
Page 73 - therefore the triangle ABC is equiangular to the triangle DEF, and it is inscribed in the circle ABC. DEF. 17. If all the sides of a rectilineal figure touch a circle lying within the figure, the circlets said to be inscribed in the figure, and the figure to be circumscribed about the circle.
Page 128 - B : Aa ratio of less inequality. Also the ratios A : B and B : A are said to be reciprocal to one another. THEOR. 1. Ratios that are equal to the same ratio are equal to one another. Let A : B :: P : Q and also
Page 113 - D + F). Props, of Mults. 3. Hence A : B : : A + C + E :B + D + F. Def. 5. or, if any number of magnitudes of the same kind be proportionals, as one of the antecedents is to its consequent, so is the sum of the antecedents to the sum of the consequents. QED COR. If A : B : : C : D (A being greater than C), then
Page 72 - 15. The circle that touches the three sides of a triangle is called the inscribed circle of the triangle. DEF. 16. A circle that touches one side of a triangle and the other two sides produced is called an escribed circle of the triangle.
Page 116 - =».FH. Hence AC : EG : : BD : FH. Def. 5. QED COR. 1. If there are three parallel straight lines, the intercepts made by them on any straight line that cuts them, are to one another in the same ratio as the
Page 85 - 28. If a chord of a circle is divided into two segments by a point in the chord or in the chord produced, the rectangle contained by these segments is equal to the difference of the squares on the radius and on the line joining the given point with the centre of the circle. Let
Page 150 - equal to the second ratio, and so on, then the first of the set is said to have to the last the ratio compounded of the original ratios. DEF. 11. When two ratios are equal, the ratio compounded of them is called the duplicate ratio of either of
Page 54 - 16, Cor. 1. QED COR. 1. The two tangents drawn to a circle from an external, point are equal, and make equal angles with the straight line joining that point and the centre. / 20, Cor. 1. COR. 2.
Page 139 - DEF. 10. If there are any number of ratios, and a set of magnitudes is taken such that the ratio of the first to the second is equal to the first -ratio, and the ratio of the second to the third is equal to the second ratio, and so on, then the first of the set is said to