## Plane Geometry |

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Page 16

George Albert Wentworth. PROPOSITION II . THEOREM . 86. If two adjacent

George Albert Wentworth. PROPOSITION II . THEOREM . 86. If two adjacent

**angles**have their**exterior**sides in a straight line , these**angles**are supplementary . A. B Let the**exterior**sides OA and OB of the adjacent**angles**AOD and BOD be in ... Page 18

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**angles**are equal . Let the lines OP and AB intersect at C. B To prove that = LOCB LACP . Proof . LOCA and OCB are supplementary . ZOCA and ACP are supplementary , 886 886 ( if two adjacent**angles**have their**exterior**sides in a straight ... Page 30

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**exterior angle**of a triangle is an angle included by one side and another side produced ; as , ACD ( Fig . 2 ) . The interior angle ACB is adjacent to the**exterior angle**; the inte- rior angles , A and B , are called opposite interior ... Page 33

... angle , or 90 ° . 136. COR . 7. In an equiangular triangle , each angle is one third of two right angles , or 60 ° . 137. COR . 8. An

... angle , or 90 ° . 136. COR . 7. In an equiangular triangle , each angle is one third of two right angles , or 60 ° . 137. COR . 8. An

**exterior angle**of a triangle is equal to the sum of the two opposite interior angles , and therefore ... Page 40

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**angle**is opposite the greater side . A E B In the triangle ACB , let AB be ...**exterior**of a △ is greater than either opposite interior △ ) , Since ZACB ...**angle**of an isosceles triangle is equal to two thirds of a right**angle**( 60 ...### Other editions - View all

### Common terms and phrases

ABē ABCD ACē adjacent angles altitude apothem base bisector bisects centre chord circumscribed circle coincide construct a square decagon diagonals diameter divided draw equiangular equidistant equilateral triangle exterior angle feet Find the area Find the locus given angle given circle given length given line given point given square given straight line given triangle greater Hence homologous sides hypotenuse inches inscribed circle intersecting isosceles trapezoid isosceles triangle limit line drawn mean proportional median middle point number of sides obtuse parallel parallelogram perimeter perpendicular PROBLEM Proof prove Q. E. D. PROPOSITION Q. E. F. Ex quadrilateral quantities radii rectangle regular polygon rhombus right angle right triangle secant segments similar polygons square equivalent straight angle tangent THEOREM third side trapezoid triangle ABC triangle is equal vertex vertices

### Popular passages

Page 94 - Any two sides of a triangle are together greater than the third side.

Page 42 - If two triangles have two sides of the one equal, respectively, to two sides of the other, but the included angle of the first greater than the included angle of the second, then the third side of the first is greater than the third side of the second.

Page 191 - The areas of two triangles which have an angle of the one equal to an angle of the other are to each other as the products of the sides including the equal angles. To prove that Proof. A Let the triangles ABC and ADE have the common angle A. A ABC -AB X AC Now and A ADE AD X AE Draw BE.

Page 156 - In a series of equal ratios, the sum of the antecedents is to the sum of the consequents as any antecedent is to its consequent.

Page 75 - PERIPHERY of a circle is its entire bounding line ; or it is a curved line, all points of which are equally distant from a point within called the centre.

Page 71 - The sum of the perpendiculars dropped from any point within an equilateral triangle to the three sides is constant, and equal to the altitude.

Page 38 - Two triangles are equal if the three sides of the one are equal respectively to the three sides of the other. In the triangles ABC and A'B'C', let AB = A'B', AC = A'C', BC=B'C'. To prove A ABC= A A'B'C'. Proof. Place A A'B'C' in the position AB'C, having its greatest side A'C' in coincidence with its equal AC, and its vertex at B', opposite B ; and draw BB'.

Page 55 - The straight line joining the middle points of two sides of a triangle is parallel to the third side and equal to half of it 46 INTERCEPTS BY PARALLEL LINES.

Page 50 - If the opposite sides of a quadrilateral are equal, the figure is a parallelogram.

Page 33 - An exterior angle of a triangle is equal to the sum of the two opposite interior angles, and therefore greater than either of them.